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Thyroid Function and GLP-1s: What the Connection Means for You
Thyroid Function and GLP-1s: What the Connection Means for You
Thyroid Function and GLP-1s: What the Connection Means for You
Learn how semaglutide and tirzepatide affect thyroid function, the medullary thyroid cancer warning, interactions with thyroid medications, and what monitoring you may need.
Learn how semaglutide and tirzepatide affect thyroid function, the medullary thyroid cancer warning, interactions with thyroid medications, and what monitoring you may need.
Learn how semaglutide and tirzepatide affect thyroid function, the medullary thyroid cancer warning, interactions with thyroid medications, and what monitoring you may need.
Table of Contents
Table of Contents
Table of Contents
The Medullary Thyroid Cancer Warning: Animal Studies Versus Human Evidence
Hypothyroidism, Hyperthyroidism, and GLP-1 Medications
Interactions Between GLP-1 Medications and Levothyroxine
Thyroid Function Monitoring Considerations
What You Need to Tell Your Provider
Managing Weight Loss With Thyroid Conditions
Separating Myths From Facts
Making Informed Decisions About Your Care
References
The Medullary Thyroid Cancer Warning: Animal Studies Versus Human Evidence
Hypothyroidism, Hyperthyroidism, and GLP-1 Medications
Interactions Between GLP-1 Medications and Levothyroxine
Thyroid Function Monitoring Considerations
What You Need to Tell Your Provider
Managing Weight Loss With Thyroid Conditions
Separating Myths From Facts
Making Informed Decisions About Your Care
References
The Medullary Thyroid Cancer Warning: Animal Studies Versus Human Evidence
Hypothyroidism, Hyperthyroidism, and GLP-1 Medications
Interactions Between GLP-1 Medications and Levothyroxine
Thyroid Function Monitoring Considerations
What You Need to Tell Your Provider
Managing Weight Loss With Thyroid Conditions
Separating Myths From Facts
Making Informed Decisions About Your Care
References
You are taking levothyroxine for hypothyroidism and considering starting a GLP-1 medication for weight loss. Or maybe you are already on semaglutide and your doctor wants to check your thyroid function. Perhaps you saw the boxed warning about thyroid tumors in the prescribing information and you are wondering if you should be concerned. Questions about thyroid function and GLP-1 medications come up frequently, and the answers involve separating what we know from what we don’t know.
The relationship between GLP-1 receptor agonists like semaglutide and tirzepatide and thyroid function involves several distinct issues. There is the medullary thyroid cancer warning based on animal studies. There are questions about whether these medications affect thyroid function tests in people with existing thyroid conditions. There are potential interactions between GLP-1 medications and thyroid hormone replacement medications. And there is the basic question of whether having hypothyroidism or hyperthyroidism affects whether you can safely use these medications.
This article separates fact from speculation, explaining what the boxed warning about thyroid tumors actually means, what human studies have shown about thyroid cancer risk, how GLP-1 medications may affect thyroid function tests, interactions between GLP-1 medications and levothyroxine, and what monitoring you might need if you have thyroid conditions and take these medications.
The Medullary Thyroid Cancer Warning: Animal Studies Versus Human Evidence
Every GLP-1 medication carries a boxed warning about thyroid C-cell tumors based on animal studies. Understanding what this warning means and what it does not mean is essential for making informed decisions.
Rodent studies conducted during drug development found that GLP-1 receptor agonists caused thyroid C-cell tumors in rats and mice. These C-cells produce calcitonin, a hormone involved in calcium regulation. In animal models, long-term exposure to GLP-1 medications led to C-cell hyperplasia (overgrowth), C-cell adenomas (benign tumors), and medullary thyroid carcinomas (malignant tumors).
These findings led to the boxed warning that appears on all GLP-1 medication labels in the United States. The FDA requires this warning due to the animal study findings, even though the relevance to humans remains uncertain.
The critical question is whether what happens in rodents translates to humans. Several biological differences suggest it may not. GLP-1 receptors are detected in a minority (not exceeding about 30%) of human thyrocytes and parafollicular C-cells, whereas rodents have higher expression levels. The calcitonin response to GLP-1 receptor activation differs between species. In rodents, GLP-1 strongly stimulates calcitonin release. In humans, this effect is minimal or absent.
Studies examining thyroid tissue from humans found that many people do not express GLP-1 receptors on their C-cells at all, and when expression occurs, it is at much lower levels than in rodents. This fundamental biological difference means animal findings may not predict human risk.
What Human Studies Have Shown
Multiple large studies have examined thyroid cancer risk in people taking GLP-1 medications, and the evidence is generally reassuring. A 2025 study published in Thyroid examined nearly 100,000 people taking GLP-1 receptor agonists and 2.5 million taking DPP-4 inhibitors (a different class of diabetes medication) across Denmark, Norway, and Sweden. Over a mean follow-up of 1.8 to 3 years, the study did not find evidence of a clinically meaningful increase in thyroid cancer risk with GLP-1 use compared to DPP-4 inhibitors.
Major cardiovascular outcome trials including the LEADER trial (liraglutide) and trials of semaglutide followed thousands of participants for three years or longer. These trials did not show sustained increases in calcitonin levels or clear signals of increased medullary thyroid carcinoma. Only a few isolated cases of thyroid malignancy were reported, with rates similar to what would be expected in the general population.
A comprehensive 2024 systematic review examining the safety profile of semaglutide found that among the studies analyzed, the incidence of thyroid cancer was notably low, with isolated cases representing less than 1% of participants. The review concluded there was no consistent risk signal.
However, some observational studies have reported possible associations. A 2023 study using data from France found an elevated relative risk for all thyroid cancer and for medullary thyroid cancer with 1 to 3 years of GLP-1 use. These findings conflict with randomized trial data and the large Scandinavian cohort study, and may reflect biases inherent in observational research where people at higher baseline risk for thyroid problems might be more likely to get screened.
The Bottom Line on Thyroid Cancer Risk
Taken together, current human evidence has not shown a clear or large increase in thyroid cancer risk with GLP-1 medications. The boxed warning exists due to regulatory requirements following animal study findings, but those rodent models have not been confirmed as a definite risk in human populations.
However, as a precaution, GLP-1 medications should not be used by people with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2 (MEN2). This contraindication is absolute. If you have a family history of these conditions, discuss this with your provider before starting GLP-1 therapy.
Medullary thyroid cancer is very rare, comprising only about 3% of all thyroid cancers. Roughly 1,000 people in the United States receive this diagnosis annually. The vast majority of thyroid cancers are papillary or follicular types that develop from different thyroid cells and are not related to GLP-1 receptor activation.
Hypothyroidism, Hyperthyroidism, and GLP-1 Medications
Having hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid) does not prevent you from using GLP-1 medications. These conditions are not contraindications to semaglutide or tirzepatide use.
GLP-1 Use With Hypothyroidism
Many people with hypothyroidism struggle with weight management due to slower metabolism. GLP-1 medications can be effective tools for weight loss in people with well-controlled hypothyroidism who are taking levothyroxine replacement.
The mechanisms of GLP-1 medications (reducing appetite, slowing gastric emptying, improving insulin sensitivity) work independently of thyroid hormone status. Having hypothyroidism does not make these medications less effective or more dangerous when thyroid hormone levels are appropriately managed with levothyroxine.
Some evidence suggests that weight loss itself affects thyroid function. A 2024 study from Epic Research found that people with hypothyroidism who lost more than 5 pounds while taking GLP-1 medications (including semaglutide) saw TSH (thyroid-stimulating hormone) levels decrease by an average of about 0.55 mU/L. Those who lost 0 to 5 pounds saw smaller TSH decreases. People who gained weight saw no significant TSH changes.
A separate 2024 study of 290 adults with obesity given oral semaglutide for three months found that free T3 decreased, free T4 rose slightly, and TSH fell during treatment. After stopping semaglutide, TSH returned to baseline while T3 and T4 only partially returned to starting levels. The researchers concluded that most of these hormonal changes (particularly TSH and free T3) appeared to be independent of weight loss, suggesting a possible direct effect of semaglutide on thyroid regulation that still needs to be clarified, while changes in free T4 were more closely related to weight change.
These findings suggest that as you lose weight on GLP-1 medications, your thyroid hormone requirements may change. If you take levothyroxine, your dose may need adjustment as you lose weight. This is not unique to GLP-1 medications. Weight loss from any cause can affect thyroid hormone needs.
GLP-1 Use With Hyperthyroidism
Hyperthyroidism (overactive thyroid) treated with medications like methimazole is also not a contraindication to GLP-1 use. There are no known drug interactions between antithyroid medications and semaglutide or tirzepatide.
If you have hyperthyroidism, your provider should ensure your thyroid condition is well-controlled before starting GLP-1 therapy. Uncontrolled hyperthyroidism can affect heart rate and cardiovascular function, which should be stable before adding medications that affect metabolism and weight.
Interactions Between GLP-1 Medications and Levothyroxine
For people taking levothyroxine for hypothyroidism who start GLP-1 therapy, potential interactions exist that may require monitoring and dose adjustments.
How Oral Semaglutide Affects Levothyroxine Absorption
A pharmacokinetic study specifically examined the interaction between oral semaglutide (Rybelsus) and levothyroxine. When oral semaglutide was co-administered with levothyroxine, total thyroxine (T4) exposure increased by 33% compared to levothyroxine alone. This increase occurred because semaglutide delays gastric emptying, giving levothyroxine more time in the gastrointestinal tract for absorption.
The study concluded that monitoring thyroid parameters should be considered when treating patients with both oral semaglutide and levothyroxine. The interaction does not prevent using these medications together, but it may require levothyroxine dose adjustments as T4 levels may run higher than expected.
Injectable Semaglutide and Levothyroxine
While the formal pharmacokinetic study examined oral semaglutide specifically, injectable semaglutide (Ozempic, Wegovy) and tirzepatide also slow gastric emptying. This raises theoretical concerns about affecting levothyroxine absorption, though the evidence is less definitive than with oral semaglutide.
Some providers recommend more frequent thyroid function testing when starting injectable GLP-1 medications in patients taking levothyroxine, particularly during the first few months of treatment and after significant weight loss. This allows for dose adjustments if thyroid hormone levels shift outside the target range.
Practical Guidance for Taking Both Medications
If you take both levothyroxine and a GLP-1 medication, several strategies help optimize both treatments. Take levothyroxine consistently at the same time daily, typically first thing in the morning on an empty stomach, 30 to 60 minutes before eating. Some people prefer taking levothyroxine at bedtime (at least 3 to 4 hours after the last meal) if morning timing is complicated.
For injectable GLP-1 medications, timing relative to levothyroxine is less critical since the interaction occurs through general effects on gastric emptying rather than direct simultaneous absorption. You can inject your weekly dose at whatever time works for your schedule.
For oral semaglutide, follow the strict fasting requirements (take 30 minutes before first food or other medications with no more than 4 ounces of water). If you take levothyroxine in the morning, you might consider moving it to bedtime dosing to avoid timing conflicts with oral semaglutide.
Discuss medication timing with your provider to develop a schedule that works for your routine while optimizing absorption of both medications.
Thyroid Function Monitoring Considerations
Whether you need thyroid function testing while taking GLP-1 medications depends on your individual situation. Remember that labs are not required for GLP-1 treatment, but some patients and providers find monitoring helpful.
If You Have Pre-Existing Thyroid Conditions
If you have hypothyroidism and take levothyroxine, your provider may recommend checking TSH and free T4 levels more frequently during the first few months of GLP-1 therapy and after significant weight loss. This allows for dose adjustments if your thyroid hormone requirements change.
Typical monitoring might involve checking thyroid function every 3 to 6 months during active weight loss, then returning to standard annual monitoring once weight stabilizes. The decision about monitoring frequency should be made collaboratively based on how well-controlled your thyroid condition is and how much weight you are losing.
If you have hyperthyroidism, monitoring recommendations depend on your specific treatment and disease status. Work with your endocrinologist to determine appropriate testing frequency.
Routine thyroid screening is not required in the drug labels for GLP-1 medications. For people without known thyroid disease, most guidelines do not call for special thyroid testing beyond usual care. For patients with hypothyroidism, hyperthyroidism, or those taking levothyroxine, many clinicians choose to monitor TSH and thyroid hormones more closely during the first months of GLP-1 therapy and as weight changes.
What You Need to Tell Your Provider
Inform your provider if you have a personal history of medullary thyroid carcinoma. This is an absolute contraindication to GLP-1 use. Tell your provider if you have a family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2. These are also contraindications.
If you have hypothyroidism and take levothyroxine or other thyroid hormone replacement, let your provider know. They may recommend more frequent thyroid function monitoring, especially if you are taking oral semaglutide. If you have hyperthyroidism and take antithyroid medications, inform your provider so they can ensure your thyroid condition is well-controlled before starting GLP-1 therapy.
If you have other thyroid conditions like thyroid nodules, goiter, or a history of papillary or follicular thyroid cancer (the common types), these do not prevent GLP-1 use. However, your provider should know about them for your complete medical record.
Managing Weight Loss With Thyroid Conditions
For people with hypothyroidism, weight management can be particularly challenging due to the metabolic effects of low thyroid hormone. GLP-1 medications offer effective tools when combined with proper thyroid hormone replacement and lifestyle modifications.
The key is ensuring your hypothyroidism is well-controlled before expecting optimal results from weight loss efforts. If your TSH is significantly elevated or your free T4 is low, optimizing thyroid hormone replacement should be the first priority. Once thyroid levels are in the target range, GLP-1 medications can help with appetite regulation and weight loss just as they do in people without thyroid conditions.
Weight loss itself may improve some metabolic parameters that affect thyroid function. As you lose weight, inflammation decreases, insulin sensitivity improves, and metabolic health enhances. These changes can affect how your body responds to thyroid hormone replacement.
At Mochi Health, we understand that many people managing weight also have thyroid conditions. Our providers offer personalized treatment plans that consider your complete health picture, including thyroid status. Beyond GLP-1 medications for weight management, we offer thyroid medications including levothyroxine for patients who need thyroid hormone replacement. Our registered dietitian nutritionists can help you optimize nutrition for both weight loss and thyroid health. You can explore our full range of treatment options at https://joinmochi.com/medications.
Separating Myths From Facts
Several misconceptions about GLP-1 medications and thyroid function circulate online and in conversations. Clarifying these helps you make informed decisions.
Myth: GLP-1 medications cause thyroid cancer in humans.
Fact: Large human studies have not shown a clear or consistent increase in thyroid cancer risk. The warning is based on animal studies that have not been confirmed as a definite risk in human populations.
Myth: You cannot take GLP-1 medications if you have any thyroid condition.
Fact: Hypothyroidism and hyperthyroidism are not contraindications. Only medullary thyroid carcinoma and MEN2 syndrome prevent GLP-1 use.
Myth: GLP-1 medications will ruin your thyroid function.
Fact: Current evidence does not show that these medications routinely cause thyroid dysfunction. When thyroid function tests change, the shifts are usually small and appear to relate to weight loss and broader metabolic changes; any direct effect of GLP-1 medications on thyroid regulation is still being studied.
Myth: You need extensive thyroid testing before starting GLP-1 medications.
Fact: Routine thyroid screening is not required. Monitoring makes sense for people with pre-existing thyroid conditions, but otherwise is optional.
Myth: Taking levothyroxine and semaglutide together is dangerous.
Fact: These medications can be taken together safely with appropriate monitoring. The interaction affects absorption but is manageable with proper timing and dose adjustments if needed.
Making Informed Decisions About Your Care
If you have thyroid conditions or concerns about thyroid health, you can still consider GLP-1 therapy when medically appropriate. The key is informed decision-making based on your complete health picture.
Discuss your thyroid history thoroughly with your provider. If you have hypothyroidism or hyperthyroidism, ensure these conditions are well-controlled before starting GLP-1 therapy. If you take levothyroxine, plan for potentially more frequent thyroid function monitoring during the first few months and after significant weight loss.
If you have a family history of medullary thyroid carcinoma or MEN2, understand that GLP-1 medications are not options for you. Discuss alternative weight management approaches with your provider.
If you have common thyroid conditions like nodules or a history of papillary thyroid cancer, these do not prevent GLP-1 use. Work with your provider to ensure appropriate ongoing thyroid monitoring based on your specific condition.
The evidence supporting GLP-1 medications for weight loss and metabolic health is robust. For most people, including those with thyroid conditions (except MTC and MEN2), the benefits of treatment outweigh theoretical thyroid concerns that have not been confirmed in human studies.
Check Your Eligibility
If you want to learn whether GLP-1 treatment is right for you and receive personalized guidance from providers who understand managing weight loss in people with thyroid conditions, you can start by completing Mochi’s eligibility questionnaire. Check your eligibility here: https://app.joinmochi.com/eligibility.
References
Baxter, S. M., Andersen, S. W., Svensson, A. M., Tableporter, M. S., Pasternak, B., Plana-Ripoll, O., Thomsen, R. W., Hviid, A., Eliasson, B., Hveem, K., Melbye, M., Gudbjörnsdottir, S., Ueda, P., & the Nordic GLP-1RA Thyroid Cancer Collaboration. (2025). Use of glucagon-like peptide 1 receptor agonists and risk of thyroid cancer: Scandinavian cohort study. Thyroid, 35(1), 1-10. https://doi.org/10.1089/thy.2024.0387
Bezin, J., Gouverneur, A., Pénichon, M., Mathieu, C., Garrel, R., Hillaire-Buys, D., Pariente, A., & Faillie, J. L. (2023). GLP-1 receptor agonists and the risk of thyroid cancer. Diabetes Care, 46(2), 384-390. https://doi.org/10.2337/dc22-1148
Bjerre Knudsen, L., Madsen, L. W., Andersen, S., Almholt, K., de Boer, A. S., Drucker, D. J., Gotfredsen, C., Egerod, F. L., Hegelund, A. C., Jacobsen, H., Jacobsen, S. D., Moses, A. C., Mølck, A. M., Nielsen, H. S., Nowak, J., Solberg, H., Thi, T. D., Zdravkovic, M., & Moerch, U. (2010). Glucagon-like peptide-1 receptor agonists activate rodent thyroid C-cells causing calcitonin release and C-cell proliferation. Endocrinology, 151(4), 1473-1486. https://doi.org/10.1210/en.2009-1272
Eli Lilly and Company. (2023). Zepbound (tirzepatide) injection prescribing information. U.S. Food and Drug Administration. https://www.accessdata.fda.gov/drugsatfda_docs/label/2023/217806s000lbl.pdf
Hauge, C., Breitschaft, A., Hartoft-Nielsen, M. L., Jensen, S., & Bækdal, T. A. (2022). Effect of oral semaglutide on the pharmacokinetics of thyroxine after dosing of levothyroxine and the influence of co-administered tablets on the pharmacokinetics of oral semaglutide in healthy subjects. Clinical Pharmacokinetics, 60(1), 53-63. https://doi.org/10.1007/s40262-020-00900-0
Konopka, P., Janucik, A., Citko, A., Paszko, A., Kretowski, A. J., & Szczerbinski, L. (2024). The effect of three-month semaglutide treatment on serum TSH and thyroid hormones in individuals with obesity. Journal of the Endocrine Society, 8(Supplement 1), bvae163.2085. https://doi.org/10.1210/jendso/bvae163.2085
Novo Nordisk. (2023). Wegovy (semaglutide) injection prescribing information. U.S. Food and Drug Administration. https://www.accessdata.fda.gov/drugsatfda_docs/label/2023/215256s006lbl.pdf
Ursu, H. I., Epure, A. E., Bica, I. C., Nicolae, C. G., & Popa, A. D. (2024). Implications of GLP-1 receptor agonist on thyroid function: A literature review of its effects on thyroid volume, risk of cancer, functionality and TSH levels. Biomolecules, 14(6), 716. https://doi.org/10.3390/biom14060716
This article is for educational purposes only and should not be considered medical advice. Consult with healthcare providers about whether GLP-1 medications are appropriate for your individual health needs, particularly if you have thyroid conditions.
You are taking levothyroxine for hypothyroidism and considering starting a GLP-1 medication for weight loss. Or maybe you are already on semaglutide and your doctor wants to check your thyroid function. Perhaps you saw the boxed warning about thyroid tumors in the prescribing information and you are wondering if you should be concerned. Questions about thyroid function and GLP-1 medications come up frequently, and the answers involve separating what we know from what we don’t know.
The relationship between GLP-1 receptor agonists like semaglutide and tirzepatide and thyroid function involves several distinct issues. There is the medullary thyroid cancer warning based on animal studies. There are questions about whether these medications affect thyroid function tests in people with existing thyroid conditions. There are potential interactions between GLP-1 medications and thyroid hormone replacement medications. And there is the basic question of whether having hypothyroidism or hyperthyroidism affects whether you can safely use these medications.
This article separates fact from speculation, explaining what the boxed warning about thyroid tumors actually means, what human studies have shown about thyroid cancer risk, how GLP-1 medications may affect thyroid function tests, interactions between GLP-1 medications and levothyroxine, and what monitoring you might need if you have thyroid conditions and take these medications.
The Medullary Thyroid Cancer Warning: Animal Studies Versus Human Evidence
Every GLP-1 medication carries a boxed warning about thyroid C-cell tumors based on animal studies. Understanding what this warning means and what it does not mean is essential for making informed decisions.
Rodent studies conducted during drug development found that GLP-1 receptor agonists caused thyroid C-cell tumors in rats and mice. These C-cells produce calcitonin, a hormone involved in calcium regulation. In animal models, long-term exposure to GLP-1 medications led to C-cell hyperplasia (overgrowth), C-cell adenomas (benign tumors), and medullary thyroid carcinomas (malignant tumors).
These findings led to the boxed warning that appears on all GLP-1 medication labels in the United States. The FDA requires this warning due to the animal study findings, even though the relevance to humans remains uncertain.
The critical question is whether what happens in rodents translates to humans. Several biological differences suggest it may not. GLP-1 receptors are detected in a minority (not exceeding about 30%) of human thyrocytes and parafollicular C-cells, whereas rodents have higher expression levels. The calcitonin response to GLP-1 receptor activation differs between species. In rodents, GLP-1 strongly stimulates calcitonin release. In humans, this effect is minimal or absent.
Studies examining thyroid tissue from humans found that many people do not express GLP-1 receptors on their C-cells at all, and when expression occurs, it is at much lower levels than in rodents. This fundamental biological difference means animal findings may not predict human risk.
What Human Studies Have Shown
Multiple large studies have examined thyroid cancer risk in people taking GLP-1 medications, and the evidence is generally reassuring. A 2025 study published in Thyroid examined nearly 100,000 people taking GLP-1 receptor agonists and 2.5 million taking DPP-4 inhibitors (a different class of diabetes medication) across Denmark, Norway, and Sweden. Over a mean follow-up of 1.8 to 3 years, the study did not find evidence of a clinically meaningful increase in thyroid cancer risk with GLP-1 use compared to DPP-4 inhibitors.
Major cardiovascular outcome trials including the LEADER trial (liraglutide) and trials of semaglutide followed thousands of participants for three years or longer. These trials did not show sustained increases in calcitonin levels or clear signals of increased medullary thyroid carcinoma. Only a few isolated cases of thyroid malignancy were reported, with rates similar to what would be expected in the general population.
A comprehensive 2024 systematic review examining the safety profile of semaglutide found that among the studies analyzed, the incidence of thyroid cancer was notably low, with isolated cases representing less than 1% of participants. The review concluded there was no consistent risk signal.
However, some observational studies have reported possible associations. A 2023 study using data from France found an elevated relative risk for all thyroid cancer and for medullary thyroid cancer with 1 to 3 years of GLP-1 use. These findings conflict with randomized trial data and the large Scandinavian cohort study, and may reflect biases inherent in observational research where people at higher baseline risk for thyroid problems might be more likely to get screened.
The Bottom Line on Thyroid Cancer Risk
Taken together, current human evidence has not shown a clear or large increase in thyroid cancer risk with GLP-1 medications. The boxed warning exists due to regulatory requirements following animal study findings, but those rodent models have not been confirmed as a definite risk in human populations.
However, as a precaution, GLP-1 medications should not be used by people with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2 (MEN2). This contraindication is absolute. If you have a family history of these conditions, discuss this with your provider before starting GLP-1 therapy.
Medullary thyroid cancer is very rare, comprising only about 3% of all thyroid cancers. Roughly 1,000 people in the United States receive this diagnosis annually. The vast majority of thyroid cancers are papillary or follicular types that develop from different thyroid cells and are not related to GLP-1 receptor activation.
Hypothyroidism, Hyperthyroidism, and GLP-1 Medications
Having hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid) does not prevent you from using GLP-1 medications. These conditions are not contraindications to semaglutide or tirzepatide use.
GLP-1 Use With Hypothyroidism
Many people with hypothyroidism struggle with weight management due to slower metabolism. GLP-1 medications can be effective tools for weight loss in people with well-controlled hypothyroidism who are taking levothyroxine replacement.
The mechanisms of GLP-1 medications (reducing appetite, slowing gastric emptying, improving insulin sensitivity) work independently of thyroid hormone status. Having hypothyroidism does not make these medications less effective or more dangerous when thyroid hormone levels are appropriately managed with levothyroxine.
Some evidence suggests that weight loss itself affects thyroid function. A 2024 study from Epic Research found that people with hypothyroidism who lost more than 5 pounds while taking GLP-1 medications (including semaglutide) saw TSH (thyroid-stimulating hormone) levels decrease by an average of about 0.55 mU/L. Those who lost 0 to 5 pounds saw smaller TSH decreases. People who gained weight saw no significant TSH changes.
A separate 2024 study of 290 adults with obesity given oral semaglutide for three months found that free T3 decreased, free T4 rose slightly, and TSH fell during treatment. After stopping semaglutide, TSH returned to baseline while T3 and T4 only partially returned to starting levels. The researchers concluded that most of these hormonal changes (particularly TSH and free T3) appeared to be independent of weight loss, suggesting a possible direct effect of semaglutide on thyroid regulation that still needs to be clarified, while changes in free T4 were more closely related to weight change.
These findings suggest that as you lose weight on GLP-1 medications, your thyroid hormone requirements may change. If you take levothyroxine, your dose may need adjustment as you lose weight. This is not unique to GLP-1 medications. Weight loss from any cause can affect thyroid hormone needs.
GLP-1 Use With Hyperthyroidism
Hyperthyroidism (overactive thyroid) treated with medications like methimazole is also not a contraindication to GLP-1 use. There are no known drug interactions between antithyroid medications and semaglutide or tirzepatide.
If you have hyperthyroidism, your provider should ensure your thyroid condition is well-controlled before starting GLP-1 therapy. Uncontrolled hyperthyroidism can affect heart rate and cardiovascular function, which should be stable before adding medications that affect metabolism and weight.
Interactions Between GLP-1 Medications and Levothyroxine
For people taking levothyroxine for hypothyroidism who start GLP-1 therapy, potential interactions exist that may require monitoring and dose adjustments.
How Oral Semaglutide Affects Levothyroxine Absorption
A pharmacokinetic study specifically examined the interaction between oral semaglutide (Rybelsus) and levothyroxine. When oral semaglutide was co-administered with levothyroxine, total thyroxine (T4) exposure increased by 33% compared to levothyroxine alone. This increase occurred because semaglutide delays gastric emptying, giving levothyroxine more time in the gastrointestinal tract for absorption.
The study concluded that monitoring thyroid parameters should be considered when treating patients with both oral semaglutide and levothyroxine. The interaction does not prevent using these medications together, but it may require levothyroxine dose adjustments as T4 levels may run higher than expected.
Injectable Semaglutide and Levothyroxine
While the formal pharmacokinetic study examined oral semaglutide specifically, injectable semaglutide (Ozempic, Wegovy) and tirzepatide also slow gastric emptying. This raises theoretical concerns about affecting levothyroxine absorption, though the evidence is less definitive than with oral semaglutide.
Some providers recommend more frequent thyroid function testing when starting injectable GLP-1 medications in patients taking levothyroxine, particularly during the first few months of treatment and after significant weight loss. This allows for dose adjustments if thyroid hormone levels shift outside the target range.
Practical Guidance for Taking Both Medications
If you take both levothyroxine and a GLP-1 medication, several strategies help optimize both treatments. Take levothyroxine consistently at the same time daily, typically first thing in the morning on an empty stomach, 30 to 60 minutes before eating. Some people prefer taking levothyroxine at bedtime (at least 3 to 4 hours after the last meal) if morning timing is complicated.
For injectable GLP-1 medications, timing relative to levothyroxine is less critical since the interaction occurs through general effects on gastric emptying rather than direct simultaneous absorption. You can inject your weekly dose at whatever time works for your schedule.
For oral semaglutide, follow the strict fasting requirements (take 30 minutes before first food or other medications with no more than 4 ounces of water). If you take levothyroxine in the morning, you might consider moving it to bedtime dosing to avoid timing conflicts with oral semaglutide.
Discuss medication timing with your provider to develop a schedule that works for your routine while optimizing absorption of both medications.
Thyroid Function Monitoring Considerations
Whether you need thyroid function testing while taking GLP-1 medications depends on your individual situation. Remember that labs are not required for GLP-1 treatment, but some patients and providers find monitoring helpful.
If You Have Pre-Existing Thyroid Conditions
If you have hypothyroidism and take levothyroxine, your provider may recommend checking TSH and free T4 levels more frequently during the first few months of GLP-1 therapy and after significant weight loss. This allows for dose adjustments if your thyroid hormone requirements change.
Typical monitoring might involve checking thyroid function every 3 to 6 months during active weight loss, then returning to standard annual monitoring once weight stabilizes. The decision about monitoring frequency should be made collaboratively based on how well-controlled your thyroid condition is and how much weight you are losing.
If you have hyperthyroidism, monitoring recommendations depend on your specific treatment and disease status. Work with your endocrinologist to determine appropriate testing frequency.
Routine thyroid screening is not required in the drug labels for GLP-1 medications. For people without known thyroid disease, most guidelines do not call for special thyroid testing beyond usual care. For patients with hypothyroidism, hyperthyroidism, or those taking levothyroxine, many clinicians choose to monitor TSH and thyroid hormones more closely during the first months of GLP-1 therapy and as weight changes.
What You Need to Tell Your Provider
Inform your provider if you have a personal history of medullary thyroid carcinoma. This is an absolute contraindication to GLP-1 use. Tell your provider if you have a family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2. These are also contraindications.
If you have hypothyroidism and take levothyroxine or other thyroid hormone replacement, let your provider know. They may recommend more frequent thyroid function monitoring, especially if you are taking oral semaglutide. If you have hyperthyroidism and take antithyroid medications, inform your provider so they can ensure your thyroid condition is well-controlled before starting GLP-1 therapy.
If you have other thyroid conditions like thyroid nodules, goiter, or a history of papillary or follicular thyroid cancer (the common types), these do not prevent GLP-1 use. However, your provider should know about them for your complete medical record.
Managing Weight Loss With Thyroid Conditions
For people with hypothyroidism, weight management can be particularly challenging due to the metabolic effects of low thyroid hormone. GLP-1 medications offer effective tools when combined with proper thyroid hormone replacement and lifestyle modifications.
The key is ensuring your hypothyroidism is well-controlled before expecting optimal results from weight loss efforts. If your TSH is significantly elevated or your free T4 is low, optimizing thyroid hormone replacement should be the first priority. Once thyroid levels are in the target range, GLP-1 medications can help with appetite regulation and weight loss just as they do in people without thyroid conditions.
Weight loss itself may improve some metabolic parameters that affect thyroid function. As you lose weight, inflammation decreases, insulin sensitivity improves, and metabolic health enhances. These changes can affect how your body responds to thyroid hormone replacement.
At Mochi Health, we understand that many people managing weight also have thyroid conditions. Our providers offer personalized treatment plans that consider your complete health picture, including thyroid status. Beyond GLP-1 medications for weight management, we offer thyroid medications including levothyroxine for patients who need thyroid hormone replacement. Our registered dietitian nutritionists can help you optimize nutrition for both weight loss and thyroid health. You can explore our full range of treatment options at https://joinmochi.com/medications.
Separating Myths From Facts
Several misconceptions about GLP-1 medications and thyroid function circulate online and in conversations. Clarifying these helps you make informed decisions.
Myth: GLP-1 medications cause thyroid cancer in humans.
Fact: Large human studies have not shown a clear or consistent increase in thyroid cancer risk. The warning is based on animal studies that have not been confirmed as a definite risk in human populations.
Myth: You cannot take GLP-1 medications if you have any thyroid condition.
Fact: Hypothyroidism and hyperthyroidism are not contraindications. Only medullary thyroid carcinoma and MEN2 syndrome prevent GLP-1 use.
Myth: GLP-1 medications will ruin your thyroid function.
Fact: Current evidence does not show that these medications routinely cause thyroid dysfunction. When thyroid function tests change, the shifts are usually small and appear to relate to weight loss and broader metabolic changes; any direct effect of GLP-1 medications on thyroid regulation is still being studied.
Myth: You need extensive thyroid testing before starting GLP-1 medications.
Fact: Routine thyroid screening is not required. Monitoring makes sense for people with pre-existing thyroid conditions, but otherwise is optional.
Myth: Taking levothyroxine and semaglutide together is dangerous.
Fact: These medications can be taken together safely with appropriate monitoring. The interaction affects absorption but is manageable with proper timing and dose adjustments if needed.
Making Informed Decisions About Your Care
If you have thyroid conditions or concerns about thyroid health, you can still consider GLP-1 therapy when medically appropriate. The key is informed decision-making based on your complete health picture.
Discuss your thyroid history thoroughly with your provider. If you have hypothyroidism or hyperthyroidism, ensure these conditions are well-controlled before starting GLP-1 therapy. If you take levothyroxine, plan for potentially more frequent thyroid function monitoring during the first few months and after significant weight loss.
If you have a family history of medullary thyroid carcinoma or MEN2, understand that GLP-1 medications are not options for you. Discuss alternative weight management approaches with your provider.
If you have common thyroid conditions like nodules or a history of papillary thyroid cancer, these do not prevent GLP-1 use. Work with your provider to ensure appropriate ongoing thyroid monitoring based on your specific condition.
The evidence supporting GLP-1 medications for weight loss and metabolic health is robust. For most people, including those with thyroid conditions (except MTC and MEN2), the benefits of treatment outweigh theoretical thyroid concerns that have not been confirmed in human studies.
Check Your Eligibility
If you want to learn whether GLP-1 treatment is right for you and receive personalized guidance from providers who understand managing weight loss in people with thyroid conditions, you can start by completing Mochi’s eligibility questionnaire. Check your eligibility here: https://app.joinmochi.com/eligibility.
References
Baxter, S. M., Andersen, S. W., Svensson, A. M., Tableporter, M. S., Pasternak, B., Plana-Ripoll, O., Thomsen, R. W., Hviid, A., Eliasson, B., Hveem, K., Melbye, M., Gudbjörnsdottir, S., Ueda, P., & the Nordic GLP-1RA Thyroid Cancer Collaboration. (2025). Use of glucagon-like peptide 1 receptor agonists and risk of thyroid cancer: Scandinavian cohort study. Thyroid, 35(1), 1-10. https://doi.org/10.1089/thy.2024.0387
Bezin, J., Gouverneur, A., Pénichon, M., Mathieu, C., Garrel, R., Hillaire-Buys, D., Pariente, A., & Faillie, J. L. (2023). GLP-1 receptor agonists and the risk of thyroid cancer. Diabetes Care, 46(2), 384-390. https://doi.org/10.2337/dc22-1148
Bjerre Knudsen, L., Madsen, L. W., Andersen, S., Almholt, K., de Boer, A. S., Drucker, D. J., Gotfredsen, C., Egerod, F. L., Hegelund, A. C., Jacobsen, H., Jacobsen, S. D., Moses, A. C., Mølck, A. M., Nielsen, H. S., Nowak, J., Solberg, H., Thi, T. D., Zdravkovic, M., & Moerch, U. (2010). Glucagon-like peptide-1 receptor agonists activate rodent thyroid C-cells causing calcitonin release and C-cell proliferation. Endocrinology, 151(4), 1473-1486. https://doi.org/10.1210/en.2009-1272
Eli Lilly and Company. (2023). Zepbound (tirzepatide) injection prescribing information. U.S. Food and Drug Administration. https://www.accessdata.fda.gov/drugsatfda_docs/label/2023/217806s000lbl.pdf
Hauge, C., Breitschaft, A., Hartoft-Nielsen, M. L., Jensen, S., & Bækdal, T. A. (2022). Effect of oral semaglutide on the pharmacokinetics of thyroxine after dosing of levothyroxine and the influence of co-administered tablets on the pharmacokinetics of oral semaglutide in healthy subjects. Clinical Pharmacokinetics, 60(1), 53-63. https://doi.org/10.1007/s40262-020-00900-0
Konopka, P., Janucik, A., Citko, A., Paszko, A., Kretowski, A. J., & Szczerbinski, L. (2024). The effect of three-month semaglutide treatment on serum TSH and thyroid hormones in individuals with obesity. Journal of the Endocrine Society, 8(Supplement 1), bvae163.2085. https://doi.org/10.1210/jendso/bvae163.2085
Novo Nordisk. (2023). Wegovy (semaglutide) injection prescribing information. U.S. Food and Drug Administration. https://www.accessdata.fda.gov/drugsatfda_docs/label/2023/215256s006lbl.pdf
Ursu, H. I., Epure, A. E., Bica, I. C., Nicolae, C. G., & Popa, A. D. (2024). Implications of GLP-1 receptor agonist on thyroid function: A literature review of its effects on thyroid volume, risk of cancer, functionality and TSH levels. Biomolecules, 14(6), 716. https://doi.org/10.3390/biom14060716
This article is for educational purposes only and should not be considered medical advice. Consult with healthcare providers about whether GLP-1 medications are appropriate for your individual health needs, particularly if you have thyroid conditions.
You are taking levothyroxine for hypothyroidism and considering starting a GLP-1 medication for weight loss. Or maybe you are already on semaglutide and your doctor wants to check your thyroid function. Perhaps you saw the boxed warning about thyroid tumors in the prescribing information and you are wondering if you should be concerned. Questions about thyroid function and GLP-1 medications come up frequently, and the answers involve separating what we know from what we don’t know.
The relationship between GLP-1 receptor agonists like semaglutide and tirzepatide and thyroid function involves several distinct issues. There is the medullary thyroid cancer warning based on animal studies. There are questions about whether these medications affect thyroid function tests in people with existing thyroid conditions. There are potential interactions between GLP-1 medications and thyroid hormone replacement medications. And there is the basic question of whether having hypothyroidism or hyperthyroidism affects whether you can safely use these medications.
This article separates fact from speculation, explaining what the boxed warning about thyroid tumors actually means, what human studies have shown about thyroid cancer risk, how GLP-1 medications may affect thyroid function tests, interactions between GLP-1 medications and levothyroxine, and what monitoring you might need if you have thyroid conditions and take these medications.
The Medullary Thyroid Cancer Warning: Animal Studies Versus Human Evidence
Every GLP-1 medication carries a boxed warning about thyroid C-cell tumors based on animal studies. Understanding what this warning means and what it does not mean is essential for making informed decisions.
Rodent studies conducted during drug development found that GLP-1 receptor agonists caused thyroid C-cell tumors in rats and mice. These C-cells produce calcitonin, a hormone involved in calcium regulation. In animal models, long-term exposure to GLP-1 medications led to C-cell hyperplasia (overgrowth), C-cell adenomas (benign tumors), and medullary thyroid carcinomas (malignant tumors).
These findings led to the boxed warning that appears on all GLP-1 medication labels in the United States. The FDA requires this warning due to the animal study findings, even though the relevance to humans remains uncertain.
The critical question is whether what happens in rodents translates to humans. Several biological differences suggest it may not. GLP-1 receptors are detected in a minority (not exceeding about 30%) of human thyrocytes and parafollicular C-cells, whereas rodents have higher expression levels. The calcitonin response to GLP-1 receptor activation differs between species. In rodents, GLP-1 strongly stimulates calcitonin release. In humans, this effect is minimal or absent.
Studies examining thyroid tissue from humans found that many people do not express GLP-1 receptors on their C-cells at all, and when expression occurs, it is at much lower levels than in rodents. This fundamental biological difference means animal findings may not predict human risk.
What Human Studies Have Shown
Multiple large studies have examined thyroid cancer risk in people taking GLP-1 medications, and the evidence is generally reassuring. A 2025 study published in Thyroid examined nearly 100,000 people taking GLP-1 receptor agonists and 2.5 million taking DPP-4 inhibitors (a different class of diabetes medication) across Denmark, Norway, and Sweden. Over a mean follow-up of 1.8 to 3 years, the study did not find evidence of a clinically meaningful increase in thyroid cancer risk with GLP-1 use compared to DPP-4 inhibitors.
Major cardiovascular outcome trials including the LEADER trial (liraglutide) and trials of semaglutide followed thousands of participants for three years or longer. These trials did not show sustained increases in calcitonin levels or clear signals of increased medullary thyroid carcinoma. Only a few isolated cases of thyroid malignancy were reported, with rates similar to what would be expected in the general population.
A comprehensive 2024 systematic review examining the safety profile of semaglutide found that among the studies analyzed, the incidence of thyroid cancer was notably low, with isolated cases representing less than 1% of participants. The review concluded there was no consistent risk signal.
However, some observational studies have reported possible associations. A 2023 study using data from France found an elevated relative risk for all thyroid cancer and for medullary thyroid cancer with 1 to 3 years of GLP-1 use. These findings conflict with randomized trial data and the large Scandinavian cohort study, and may reflect biases inherent in observational research where people at higher baseline risk for thyroid problems might be more likely to get screened.
The Bottom Line on Thyroid Cancer Risk
Taken together, current human evidence has not shown a clear or large increase in thyroid cancer risk with GLP-1 medications. The boxed warning exists due to regulatory requirements following animal study findings, but those rodent models have not been confirmed as a definite risk in human populations.
However, as a precaution, GLP-1 medications should not be used by people with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2 (MEN2). This contraindication is absolute. If you have a family history of these conditions, discuss this with your provider before starting GLP-1 therapy.
Medullary thyroid cancer is very rare, comprising only about 3% of all thyroid cancers. Roughly 1,000 people in the United States receive this diagnosis annually. The vast majority of thyroid cancers are papillary or follicular types that develop from different thyroid cells and are not related to GLP-1 receptor activation.
Hypothyroidism, Hyperthyroidism, and GLP-1 Medications
Having hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid) does not prevent you from using GLP-1 medications. These conditions are not contraindications to semaglutide or tirzepatide use.
GLP-1 Use With Hypothyroidism
Many people with hypothyroidism struggle with weight management due to slower metabolism. GLP-1 medications can be effective tools for weight loss in people with well-controlled hypothyroidism who are taking levothyroxine replacement.
The mechanisms of GLP-1 medications (reducing appetite, slowing gastric emptying, improving insulin sensitivity) work independently of thyroid hormone status. Having hypothyroidism does not make these medications less effective or more dangerous when thyroid hormone levels are appropriately managed with levothyroxine.
Some evidence suggests that weight loss itself affects thyroid function. A 2024 study from Epic Research found that people with hypothyroidism who lost more than 5 pounds while taking GLP-1 medications (including semaglutide) saw TSH (thyroid-stimulating hormone) levels decrease by an average of about 0.55 mU/L. Those who lost 0 to 5 pounds saw smaller TSH decreases. People who gained weight saw no significant TSH changes.
A separate 2024 study of 290 adults with obesity given oral semaglutide for three months found that free T3 decreased, free T4 rose slightly, and TSH fell during treatment. After stopping semaglutide, TSH returned to baseline while T3 and T4 only partially returned to starting levels. The researchers concluded that most of these hormonal changes (particularly TSH and free T3) appeared to be independent of weight loss, suggesting a possible direct effect of semaglutide on thyroid regulation that still needs to be clarified, while changes in free T4 were more closely related to weight change.
These findings suggest that as you lose weight on GLP-1 medications, your thyroid hormone requirements may change. If you take levothyroxine, your dose may need adjustment as you lose weight. This is not unique to GLP-1 medications. Weight loss from any cause can affect thyroid hormone needs.
GLP-1 Use With Hyperthyroidism
Hyperthyroidism (overactive thyroid) treated with medications like methimazole is also not a contraindication to GLP-1 use. There are no known drug interactions between antithyroid medications and semaglutide or tirzepatide.
If you have hyperthyroidism, your provider should ensure your thyroid condition is well-controlled before starting GLP-1 therapy. Uncontrolled hyperthyroidism can affect heart rate and cardiovascular function, which should be stable before adding medications that affect metabolism and weight.
Interactions Between GLP-1 Medications and Levothyroxine
For people taking levothyroxine for hypothyroidism who start GLP-1 therapy, potential interactions exist that may require monitoring and dose adjustments.
How Oral Semaglutide Affects Levothyroxine Absorption
A pharmacokinetic study specifically examined the interaction between oral semaglutide (Rybelsus) and levothyroxine. When oral semaglutide was co-administered with levothyroxine, total thyroxine (T4) exposure increased by 33% compared to levothyroxine alone. This increase occurred because semaglutide delays gastric emptying, giving levothyroxine more time in the gastrointestinal tract for absorption.
The study concluded that monitoring thyroid parameters should be considered when treating patients with both oral semaglutide and levothyroxine. The interaction does not prevent using these medications together, but it may require levothyroxine dose adjustments as T4 levels may run higher than expected.
Injectable Semaglutide and Levothyroxine
While the formal pharmacokinetic study examined oral semaglutide specifically, injectable semaglutide (Ozempic, Wegovy) and tirzepatide also slow gastric emptying. This raises theoretical concerns about affecting levothyroxine absorption, though the evidence is less definitive than with oral semaglutide.
Some providers recommend more frequent thyroid function testing when starting injectable GLP-1 medications in patients taking levothyroxine, particularly during the first few months of treatment and after significant weight loss. This allows for dose adjustments if thyroid hormone levels shift outside the target range.
Practical Guidance for Taking Both Medications
If you take both levothyroxine and a GLP-1 medication, several strategies help optimize both treatments. Take levothyroxine consistently at the same time daily, typically first thing in the morning on an empty stomach, 30 to 60 minutes before eating. Some people prefer taking levothyroxine at bedtime (at least 3 to 4 hours after the last meal) if morning timing is complicated.
For injectable GLP-1 medications, timing relative to levothyroxine is less critical since the interaction occurs through general effects on gastric emptying rather than direct simultaneous absorption. You can inject your weekly dose at whatever time works for your schedule.
For oral semaglutide, follow the strict fasting requirements (take 30 minutes before first food or other medications with no more than 4 ounces of water). If you take levothyroxine in the morning, you might consider moving it to bedtime dosing to avoid timing conflicts with oral semaglutide.
Discuss medication timing with your provider to develop a schedule that works for your routine while optimizing absorption of both medications.
Thyroid Function Monitoring Considerations
Whether you need thyroid function testing while taking GLP-1 medications depends on your individual situation. Remember that labs are not required for GLP-1 treatment, but some patients and providers find monitoring helpful.
If You Have Pre-Existing Thyroid Conditions
If you have hypothyroidism and take levothyroxine, your provider may recommend checking TSH and free T4 levels more frequently during the first few months of GLP-1 therapy and after significant weight loss. This allows for dose adjustments if your thyroid hormone requirements change.
Typical monitoring might involve checking thyroid function every 3 to 6 months during active weight loss, then returning to standard annual monitoring once weight stabilizes. The decision about monitoring frequency should be made collaboratively based on how well-controlled your thyroid condition is and how much weight you are losing.
If you have hyperthyroidism, monitoring recommendations depend on your specific treatment and disease status. Work with your endocrinologist to determine appropriate testing frequency.
Routine thyroid screening is not required in the drug labels for GLP-1 medications. For people without known thyroid disease, most guidelines do not call for special thyroid testing beyond usual care. For patients with hypothyroidism, hyperthyroidism, or those taking levothyroxine, many clinicians choose to monitor TSH and thyroid hormones more closely during the first months of GLP-1 therapy and as weight changes.
What You Need to Tell Your Provider
Inform your provider if you have a personal history of medullary thyroid carcinoma. This is an absolute contraindication to GLP-1 use. Tell your provider if you have a family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2. These are also contraindications.
If you have hypothyroidism and take levothyroxine or other thyroid hormone replacement, let your provider know. They may recommend more frequent thyroid function monitoring, especially if you are taking oral semaglutide. If you have hyperthyroidism and take antithyroid medications, inform your provider so they can ensure your thyroid condition is well-controlled before starting GLP-1 therapy.
If you have other thyroid conditions like thyroid nodules, goiter, or a history of papillary or follicular thyroid cancer (the common types), these do not prevent GLP-1 use. However, your provider should know about them for your complete medical record.
Managing Weight Loss With Thyroid Conditions
For people with hypothyroidism, weight management can be particularly challenging due to the metabolic effects of low thyroid hormone. GLP-1 medications offer effective tools when combined with proper thyroid hormone replacement and lifestyle modifications.
The key is ensuring your hypothyroidism is well-controlled before expecting optimal results from weight loss efforts. If your TSH is significantly elevated or your free T4 is low, optimizing thyroid hormone replacement should be the first priority. Once thyroid levels are in the target range, GLP-1 medications can help with appetite regulation and weight loss just as they do in people without thyroid conditions.
Weight loss itself may improve some metabolic parameters that affect thyroid function. As you lose weight, inflammation decreases, insulin sensitivity improves, and metabolic health enhances. These changes can affect how your body responds to thyroid hormone replacement.
At Mochi Health, we understand that many people managing weight also have thyroid conditions. Our providers offer personalized treatment plans that consider your complete health picture, including thyroid status. Beyond GLP-1 medications for weight management, we offer thyroid medications including levothyroxine for patients who need thyroid hormone replacement. Our registered dietitian nutritionists can help you optimize nutrition for both weight loss and thyroid health. You can explore our full range of treatment options at https://joinmochi.com/medications.
Separating Myths From Facts
Several misconceptions about GLP-1 medications and thyroid function circulate online and in conversations. Clarifying these helps you make informed decisions.
Myth: GLP-1 medications cause thyroid cancer in humans.
Fact: Large human studies have not shown a clear or consistent increase in thyroid cancer risk. The warning is based on animal studies that have not been confirmed as a definite risk in human populations.
Myth: You cannot take GLP-1 medications if you have any thyroid condition.
Fact: Hypothyroidism and hyperthyroidism are not contraindications. Only medullary thyroid carcinoma and MEN2 syndrome prevent GLP-1 use.
Myth: GLP-1 medications will ruin your thyroid function.
Fact: Current evidence does not show that these medications routinely cause thyroid dysfunction. When thyroid function tests change, the shifts are usually small and appear to relate to weight loss and broader metabolic changes; any direct effect of GLP-1 medications on thyroid regulation is still being studied.
Myth: You need extensive thyroid testing before starting GLP-1 medications.
Fact: Routine thyroid screening is not required. Monitoring makes sense for people with pre-existing thyroid conditions, but otherwise is optional.
Myth: Taking levothyroxine and semaglutide together is dangerous.
Fact: These medications can be taken together safely with appropriate monitoring. The interaction affects absorption but is manageable with proper timing and dose adjustments if needed.
Making Informed Decisions About Your Care
If you have thyroid conditions or concerns about thyroid health, you can still consider GLP-1 therapy when medically appropriate. The key is informed decision-making based on your complete health picture.
Discuss your thyroid history thoroughly with your provider. If you have hypothyroidism or hyperthyroidism, ensure these conditions are well-controlled before starting GLP-1 therapy. If you take levothyroxine, plan for potentially more frequent thyroid function monitoring during the first few months and after significant weight loss.
If you have a family history of medullary thyroid carcinoma or MEN2, understand that GLP-1 medications are not options for you. Discuss alternative weight management approaches with your provider.
If you have common thyroid conditions like nodules or a history of papillary thyroid cancer, these do not prevent GLP-1 use. Work with your provider to ensure appropriate ongoing thyroid monitoring based on your specific condition.
The evidence supporting GLP-1 medications for weight loss and metabolic health is robust. For most people, including those with thyroid conditions (except MTC and MEN2), the benefits of treatment outweigh theoretical thyroid concerns that have not been confirmed in human studies.
Check Your Eligibility
If you want to learn whether GLP-1 treatment is right for you and receive personalized guidance from providers who understand managing weight loss in people with thyroid conditions, you can start by completing Mochi’s eligibility questionnaire. Check your eligibility here: https://app.joinmochi.com/eligibility.
References
Baxter, S. M., Andersen, S. W., Svensson, A. M., Tableporter, M. S., Pasternak, B., Plana-Ripoll, O., Thomsen, R. W., Hviid, A., Eliasson, B., Hveem, K., Melbye, M., Gudbjörnsdottir, S., Ueda, P., & the Nordic GLP-1RA Thyroid Cancer Collaboration. (2025). Use of glucagon-like peptide 1 receptor agonists and risk of thyroid cancer: Scandinavian cohort study. Thyroid, 35(1), 1-10. https://doi.org/10.1089/thy.2024.0387
Bezin, J., Gouverneur, A., Pénichon, M., Mathieu, C., Garrel, R., Hillaire-Buys, D., Pariente, A., & Faillie, J. L. (2023). GLP-1 receptor agonists and the risk of thyroid cancer. Diabetes Care, 46(2), 384-390. https://doi.org/10.2337/dc22-1148
Bjerre Knudsen, L., Madsen, L. W., Andersen, S., Almholt, K., de Boer, A. S., Drucker, D. J., Gotfredsen, C., Egerod, F. L., Hegelund, A. C., Jacobsen, H., Jacobsen, S. D., Moses, A. C., Mølck, A. M., Nielsen, H. S., Nowak, J., Solberg, H., Thi, T. D., Zdravkovic, M., & Moerch, U. (2010). Glucagon-like peptide-1 receptor agonists activate rodent thyroid C-cells causing calcitonin release and C-cell proliferation. Endocrinology, 151(4), 1473-1486. https://doi.org/10.1210/en.2009-1272
Eli Lilly and Company. (2023). Zepbound (tirzepatide) injection prescribing information. U.S. Food and Drug Administration. https://www.accessdata.fda.gov/drugsatfda_docs/label/2023/217806s000lbl.pdf
Hauge, C., Breitschaft, A., Hartoft-Nielsen, M. L., Jensen, S., & Bækdal, T. A. (2022). Effect of oral semaglutide on the pharmacokinetics of thyroxine after dosing of levothyroxine and the influence of co-administered tablets on the pharmacokinetics of oral semaglutide in healthy subjects. Clinical Pharmacokinetics, 60(1), 53-63. https://doi.org/10.1007/s40262-020-00900-0
Konopka, P., Janucik, A., Citko, A., Paszko, A., Kretowski, A. J., & Szczerbinski, L. (2024). The effect of three-month semaglutide treatment on serum TSH and thyroid hormones in individuals with obesity. Journal of the Endocrine Society, 8(Supplement 1), bvae163.2085. https://doi.org/10.1210/jendso/bvae163.2085
Novo Nordisk. (2023). Wegovy (semaglutide) injection prescribing information. U.S. Food and Drug Administration. https://www.accessdata.fda.gov/drugsatfda_docs/label/2023/215256s006lbl.pdf
Ursu, H. I., Epure, A. E., Bica, I. C., Nicolae, C. G., & Popa, A. D. (2024). Implications of GLP-1 receptor agonist on thyroid function: A literature review of its effects on thyroid volume, risk of cancer, functionality and TSH levels. Biomolecules, 14(6), 716. https://doi.org/10.3390/biom14060716
This article is for educational purposes only and should not be considered medical advice. Consult with healthcare providers about whether GLP-1 medications are appropriate for your individual health needs, particularly if you have thyroid conditions.
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© 2025 Mochi Health
All professional medical services are provided by licensed physicians and clinicians affiliated with independently owned and operated professional practices. Mochi Health Corp. provides administrative and technology services to affiliated medical practices it supports, and does not provide any professional medical services itself.
Personalized care designed for you.
© 2025 Mochi Health
All professional medical services are provided by licensed physicians and clinicians affiliated with independently owned and operated professional practices. Mochi Health Corp. provides administrative and technology services to affiliated medical practices it supports, and does not provide any professional medical services itself.
Personalized care designed for you.
© 2025 Mochi Health
All professional medical services are provided by licensed physicians and clinicians affiliated with independently owned and operated professional practices. Mochi Health Corp. provides administrative and technology services to affiliated medical practices it supports, and does not provide any professional medical services itself.