Deep Dive: What you need to know about GLP-1s when you have Hashimoto's and hypothyroidism

Diana H. Szucs, PharmD | Krisna Bhargava, PhD (Founder & CEO at EXPIN) | Uta Guo, MD (Head of Medicine at EXPIN)

The science is still out, but there's enough of it to help you think through the risks and rewards.

GLP-1–based medications such as semaglutide (Ozempic/Wegovy) and tirzepatide (Mounjaro/Zepbound) have transformed the treatment of obesity and metabolic disease. For people with Hashimoto’s or hypothyroidism, weight management can already be complicated—not only because of changes in metabolism, but also because hypothyroidism can contribute to fluid retention and changes on the scale. It's no surprise these medications have generated widespread interest, along with a very specific set of questions, in these communities.

Will they still work if your thyroid is underactive? Could losing weight change your levothyroxine dose? What about the thyroid cancer warning? Can GLP-1s affect thyroid autoimmunity—or perhaps even reduce inflammation? And how can you tell whether a new symptom is coming from the medication, your thyroid, or something else entirely?

In discussions on Reddit, Instagram, TikTok, etc., the answers can be difficult to sort through. There are people who feel dramatically better, people who feel worse, warnings about thyroid cancer, advice passed along from someone else’s endocrinologist, and individual studies shared without much context.

The problem is that an anecdote, a single study, and a well-established clinical finding do not carry the same weight.

At EXPIN, we recently added GLP-1 medications to the medical exposures we track alongside environmental and lifestyle exposures.

Map your exposures →

For this guide, we took the questions people are actually asking online and looked at what the scientific evidence can—and cannot—tell us today. Before we get into the individual questions, here are the big takeaways.

What you need to know

• When properly managed, hypothyroidism does not seem to interfere with the effectiveness of GLP-1 medications for weight loss.
• Your levothyroxine needs may change as you lose weight. GLP-1 treatment has also been associated with changes in TSH, so closer thyroid monitoring may be useful while your weight and treatment are changing.
• Oral semaglutide can increase levothyroxine levels in the bloodstream. Whether injectable GLP-1 medications meaningfully change levothyroxine absorption is still being studied.
• Hashimoto’s is not the thyroid condition associated with the GLP-1 boxed cancer warning. That warning specifically addresses medullary thyroid carcinoma (MTC) and Multiple Endocrine Neoplasia type 2 (MEN2).
• GLP-1 medications seem to lower systemic inflammation, but it is still unclear if they enhance or impair Hashimoto’s autoimmunity.
• Nutrition matters. A much smaller appetite can mean inadequate calories, protein, iron, vitamin D, B vitamins, and other nutrients, and many of the resulting symptoms can look a lot like thyroid symptoms.

What’s actionable right now?

If you take levothyroxine, don’t change your dose or routine on your own when starting a GLP-1. Instead, discuss a thyroid-monitoring plan with your clinician; depending on your situation, that may include checking TSH as early as about 6–8 weeks after starting treatment and again as substantial weight loss or medication changes occur. Keep your levothyroxine routine consistent, pay attention to significant changes in symptoms or food intake, and make sure your prescriber knows about any personal or family history of MTC or MEN2.

Now we'll dive into my specific questions. Under each question, you will see an "evidence rating" that tells you our gauge on how trustworthy the science is *today.

Evidence ratings	What they mean
STRONG	Multiple randomized trials or large meta-analyses pointing toward the same conclusion
MODERATE	Consistent findings across good observational studies, or one well-designed trial
LIMITED	Small studies, conflicting results, or findings that could be explained by bias
CONFLICTING	Credible research points in opposite directions and the question is genuinely open
MECHANISM ONLY	Biologically plausible based on how the body works, but not directly tested in people

Table of Contents

01. Will a GLP-1 work if my thyroid is underactive?
02. Can people really drop that much weight in one week?
03. How does going on a GLP-1 impact my levothyroxine dose?
04. Could my thyroid numbers move for reasons that have nothing to do with my weight?
05. Does a GLP-1 mess with how I absorb my levothyroxine?
06. Should I change how I take my levothyroxine?
07. The box mentions thyroid cancer. Should I be worried?
08. Does having Hashimoto's put me in the group the warning is about?
09. What about ordinary thyroid cancer, the common kind?
10. I have thyroid nodules. Will a GLP-1 make them grow?
11. Can a GLP-1 trigger or worsen thyroid autoimmunity?
12. Could a GLP-1 actually help my autoimmunity? My inflammation?
13. I'm barely eating. Does that matter? I heard that can impact my thyroid.
14. Which micronutrient and mineral deficiencies should I watch for, and why do they matter for my thyroid?
15. Does losing fat quickly release stored chemicals into my blood?
16. How do I tell whether a symptom is because of abnormal thyroid levels or the GLP-1?
17. How often should my thyroid be rechecked?
18. How do I apply this information to my case?

01. Will a GLP-1 work if my thyroid is underactive?

Yes, about as well as it works for anyone else, as long as your thyroid is adequately treated.

Evidence: MODERATE

A 2025 study compared individuals taking liraglutide for obesity who had well-managed hypothyroidism and individuals without thyroid issues. Both groups experienced similar weight and body fat loss And within the hypothyroid group, sitting at the higher or lower end of the normal TSH range made no difference to how much came off.[1]

What would make this stronger: This was a retrospective study focused on liraglutide, a now older GLP-1 drug. Conducting larger studies, especially those including semaglutide and tirzepatide, would strengthen the confidence in the conclusions.

02. Can people really drop that much weight in one week?

Yes—but a large early drop is usually not all body fat. Much of it is water and glycogen, the stored form of carbohydrate your body keeps for quick energy.

Evidence: STRONG

When you suddenly eat less, your body begins using glycogen stores. Glycogen holds water, so as those stores decrease, water is lost along with them. This is why the scale can move quickly during the first few weeks of weight loss. [2–4]

People with hypothyroidism can also retain more fluid at baseline, so some may notice an especially noticeable early change as weight loss begins. Over time, however, the composition of weight loss shifts and a greater proportion comes from body fat.

Researchers have measured this effect directly and found that in the opening 4-6 weeks of weight loss, what the body sheds looks very different than what comes off later.[2] One study tracked healthy men through ten days of fasting and worked out where the lost tissue actually came from: water and glycogen accounted for well over half of it.[3] Another tracked women placed on a very low calorie diet: muscle glycogen fell measurably within the first week. However, when placed on a gentler diet over six months, what came off was almost entirely fat.[4]

So an unusually large first-week drop does not mean you are losing body fat that quickly—and it is better to judge the longer-term response over weeks to months rather than from the first few days.

03. How does going on a GLP-1 impact my levothyroxine dose?

Once you lose a meaningful amount of weight, your dose will need to change.

Evidence: STRONG that weight loss lowers how much thyroid hormone you need, and that monitoring is not keeping pace. MODERATE that GLP-1s specifically can contribute to changes in thyroid hormone requirements, although we still don't know how much adjustment is typically needed.

Levothyroxine is prescribed based partly on body size and composition, so significant weight loss can make a previously stable dose no longer appropriate. This has been well documented after bariatric surgery, where thyroid hormone requirements often change as body weight changes. [5,6]

Recent evidence indicates that a similar pattern might happen during GLP-1 therapy. Studies involving individuals with hypothyroidism on levothyroxine have shown decreases in TSH levels after initiating GLP-1–based drugs, implying that thyroid hormone needs can change during treatment. More extensive prospective research is needed to understand how frequently dose adjustments are required and the typical magnitude of these changes.

The key point is that a levothyroxine dose that was appropriate before significant weight loss might no longer be correct afterward. We still lack precise information on how often adjustments are needed, their typical magnitude, or whether changes are mainly due to weight loss or other effects of GLP-1 medications.

Symptoms of too much thyroid hormone can include palpitations, anxiety, trouble sleeping, feeling unusually hot, or tremor, but symptoms alone cannot tell you whether your dose needs adjusting. If you take levothyroxine, discuss a thyroid-monitoring plan with your doctor when starting a GLP-1. Depending on your situation, that may include checking TSH as early as about six weeks after starting treatment and repeating it as significant weight loss or medication changes occur.

04. Could my thyroid numbers move for reasons that have nothing to do with my weight?

Yes. Thyroid test results can change for many reasons unrelated to weight or GLP-1 treatment, while weight changes and potentially the GLP-1 medication itself can also play a role.

Evidence: STRONG that factors such as medication absorption or interactions, supplements, illness, hormonal changes, and normal biological variation can affect thyroid test results. STRONG that excess weight and weight loss can also influence TSH. LIMITED on whether GLP-1 medications have a separate, direct effect on thyroid function.

Thyroid test results can fluctuate due to reasons entirely unrelated to weight or GLP-1 therapy. Factors such as changes in levothyroxine intake or absorption, interactions with medications or supplements like iron and calcium, pregnancy, estrogen fluctuations, acute illness, and natural biological variation can all impact thyroid measurements. [12] Additionally, biotin supplements may interfere with certain thyroid tests, causing false abnormalities despite unchanged thyroid function. [12,13]

Weight can also play a role. Obesity itself can be associated with mildly higher TSH, even in people without underlying thyroid disease, and weight loss tends to bring those levels down.9,10

GLP-1 treatment has also been associated with lower TSH in several studies. In some, the change closely followed the amount of weight lost, while other studies suggest there may be additional effects on thyroid regulation.[11]

We know that each of the factors above can influence thyroid test results. The challenge is that they often happen simultaneously: weight loss can alter thyroid hormone needs, medication absorption may shift, and a GLP-1 may have additional effects of its own. In a complex biological system, these effects can overlap or add together, making it difficult to determine how much of a particular change in TSH is coming from any one factor.

05. Does a GLP-1 mess with how I absorb my levothyroxine?

It can—but the strongest evidence comes from studies of oral semaglutide. For injectable GLP-1s, the effect on levothyroxine absorption is still being assessed.

Evidence: MODERATE that oral semaglutide can increase the amount of levothyroxine absorbed into the bloodstream. LIMITED on how injectable GLP-1 medications affect levothyroxine absorption specifically.

GLP-1 medications generally delay gastric emptying, causing food and medicines to stay in the stomach longer. Since levothyroxine absorption depends on gastrointestinal conditions and timing, this could lead to an interaction between the two medications.

The interaction between oral semaglutide and levothyroxine has been directly studied. When taken together, the total thyroxine level in the blood increased by approximately one-third compared to taking levothyroxine alone.[14,15] The current prescribing information highlights this interaction and advises monitoring of oral medications that need close clinical or laboratory follow-up.

For injectable semaglutide and other GLP-1–based medications, delayed gastric emptying may impact levothyroxine absorption. Current prescribing guidance indicates that the absorption of oral medications could be affected.[18] Clinical reports also suggest changes in thyroid levels following injectable GLP-1 therapy,[16], [8] but there are no dedicated pharmacokinetic studies yet quantifying how much these medications influence levothyroxine absorption.

So if your thyroid levels shift after starting a GLP-1, altered levothyroxine absorption might be a factor—but it's also important to consider the impacts of weight loss and changing thyroid hormone needs mentioned earlier. This underscores the importance of discussing more frequent TSH testing with your healthcare provider when starting or adjusting GLP-1 treatments, especially with oral semaglutide.

06. Should I change how I take my levothyroxine?

No. Do not change your levothyroxine dose, timing, or formulation on your own just because you are starting a GLP-1 medication. Continue taking it as prescribed, and contact your doctor if you notice new or worsening symptoms.

Evidence: STRONG for the usual levothyroxine administration rules. MODERATE that oral semaglutide requires special consideration because of its dosing requirements and documented interaction with levothyroxine. LIMITED on whether injectable GLP-1 medications require any change in how levothyroxine is taken.

Levothyroxine absorption is sensitive to food, supplements, medications, and timing, so consistency is important—especially when other factors such as weight or GLP-1 treatment are changing.[17]

• Take levothyroxine consistently on an empty stomach with water and wait 30–60 minutes before eating.[17]
• Take calcium and iron supplements at least four hours apart, as they can interfere with the absorption of levothyroxine.[17]
• Be boringly consistent — same time, same conditions, every day. Consistency is important to make sure any changes in thyroid blood tests are easier to interpret.
• If you're taking oral semaglutide, consult your doctor or pharmacist about how to space it from other medications. Both should be taken on an empty stomach, and oral semaglutide may raise levothyroxine levels in the blood.[15]
• Don't switch brands or formulations without telling your doctor

For injectable GLP-1 medications, there is currently no established recommendation to change how levothyroxine is taken. The priority is consistency and appropriate thyroid monitoring rather than changing your routine on your own.

07. The box mentions thyroid cancer. Should I be worried?

The warning is real, but it is very specific. It relates to one rare cancer seen in rodents, and it's still unclear whether the same risk translates to humans

Evidence: STRONG that GLP-1–based medications can cause thyroid C-cell tumors in rodents. MODERATE that human evidence so far is reassuring, but the long-term risk of medullary thyroid carcinoma in humans has not been definitively established.

The boxed warning exists because rodents exposed to GLP-1–based medications developed tumors in thyroid C cells, the cells involved in a rare thyroid cancer called medullary thyroid carcinoma (MTC).[18], [19]

Rodents and humans differ biologically. Human thyroid C cells appear to have much less GLP-1 receptor activity, and clinical studies have not shown the same clear C-cell response seen in rodents.[19],[20] The FDA still considers the relevance of the animal findings to humans unknown, so the warning remains in place.[18]

For now, the most important thing is to understand what the warning is about: medullary thyroid carcinoma and Multiple Endocrine Neoplasia type 2 (MEN2)—not thyroid disease in general. We’ll look specifically at what that means for someone with Hashimoto’s in the next question.

08. Does having Hashimoto's put me in the group the warning is about?

No. Hashimoto’s by itself does not put you in the group covered by the GLP-1 thyroid cancer warning.

Evidence: STRONG

The warning specifically applies to people with a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia type 2 (MEN2). [18]

Hashimoto’s is a different disease involving a different part of the thyroid. It is an autoimmune condition that primarily damages the thyroid’s hormone-producing follicular cells, while MTC develops from C cells, which produce the hormone calcitonin.[21]

So having Hashimoto’s, elevated thyroid antibodies, or hypothyroidism does not by itself place someone in the contraindicated group. A personal or family history of MTC or MEN2 is what matters for this specific warning.[18]

09. What about ordinary thyroid cancer, the common kind?

This question is not completely settled, although the larger and more recent studies are reassuring.

Evidence: CONFLICTING

Some studies have reported a small increase in thyroid cancer diagnoses among people taking GLP-1 medications, including a French population study and a meta-analysis of randomized trials.[22,23] However, thyroid cancer was rare in the trials, making the estimates imprecise, and other large population studies have found no increased risk.[24], [25]

One reason the studies may disagree is detection bias. People starting GLP-1 medications may have more medical visits and testing, making small thyroid cancers more likely to be discovered. This matters because many thyroid cancers grow slowly and may never have caused symptoms during a person's lifetime.[26]

Overall, the evidence does not currently establish that GLP-1 medications cause differentiated thyroid cancer, but longer follow-up is still needed. These drugs have not been used at today's scale for decades, so a very small or very long-term risk cannot yet be completely ruled out.[25], [[26]] (26)

10. I have thyroid nodules. Will a GLP-1 make them grow?

We don't currently have good evidence that GLP-1 medications cause thyroid nodules to grow.

Evidence: LIMITED

Thyroid nodules often change size over time, regardless of GLP-1 usage. In a 12-month study, nodules grew slightly in both groups—those on GLP-1 medications and those not. The researchers found no significant link between GLP-1 treatment and nodule expansion.[27]

The evidence remains limited, so we cannot entirely dismiss the possibility of an effect. However, current expert recommendations do not suggest additional thyroid ultrasounds or specific nodule monitoring solely due to starting a GLP-1. Existing nodules should still be assessed and monitored following standard thyroid nodule guidelines. [28]

11. Can a GLP-1 trigger or worsen thyroid autoimmunity?

The jury is still out on this one. Some observational studies have found a small increase in autoimmune thyroiditis, while other evidence has not shown a clear increased risk.

Evidence: CONFLICTING

Recent real-world studies have identified a potential signal, especially in individuals with type 2 diabetes.[29], [30] However, a meta-analysis of 45 randomized clinical trials showed no significant rise in thyroiditis or hypothyroidism associated with GLP-1 medications, although thyroid events were rare and a small effect might have gone undetected. [31]

Most importantly, there are still no solid studies on individuals with existing Hashimoto’s. It remains unclear whether GLP-1 treatments affect thyroid antibodies, autoimmune activity, or the progression of established disease. Currently, the evidence does not definitively show that GLP-1 medications either trigger or worsen Hashimoto’s, but it is also not strong enough to dismiss any potential effect.

12. Could a GLP-1 actually help my autoimmunity? My inflammation?

GLP-1 medications do appear to reduce some types of systemic inflammation. Whether that translates into improvement in Hashimoto’s autoimmunity is still unknown.

Evidence: MODERATE to STRONG for an anti-inflammatory effect. LIMITED and CONFLICTING on autoimmune disease, and no direct evidence yet that GLP-1 treatment improves established Hashimoto’s.

Across randomized trials, GLP-1 medications consistently reduce C-reactive protein (CRP), a marker of systemic inflammation, although effects on other inflammatory markers such as IL-6 and TNF-α have been more variable.[32]

There is also biological evidence that GLP-1 signaling can interact directly with immune cells, including T cells, suggesting that these medications may influence immune regulation beyond their effects on weight and blood sugar.[33] Genetic studies also suggest possible effects on autoimmune disease, but the findings are mixed rather than uniformly protective.[34], [35]

The important distinction is that reducing systemic inflammation is not the same as treating Hashimoto’s. We do not yet have clinical trials showing that GLP-1 medications lower thyroid antibodies, slow autoimmune damage to the thyroid, or preserve thyroid function in people who already have Hashimoto’s.

13. I'm barely eating. Does that matter? I heard that can impact my thyroid.

Yes. Eating substantially less for a prolonged period can affect thyroid hormone levels, even when the thyroid gland itself has not become less functional.

Evidence: MODERATE

GLP-1 medications can suppress appetite enough that some people unintentionally eat very little. In one 2026 study, adults taking GLP-1–based medications reported an average intake of about 750 calories per day, with particularly low protein intake.[36] This was a self-selected group, so that number should not be assumed to represent everyone taking these medications.

Calorie restriction itself can also change thyroid physiology. Studies have found that prolonged calorie restriction and weight loss can lower T3, the active thyroid hormone, as the body adapts to reduced energy availability.[37]

If appetite becomes extremely low, the concern is not simply the number on the scale. Adequate calories, protein, and overall nutrition still matter, particularly because symptoms of under-eating—fatigue, weakness, feeling cold, hair loss, or brain fog—can easily be mistaken for worsening hypothyroidism.

14. Which micronutrient and mineral deficiencies should I watch for, and why do they matter for my thyroid?

Vitamin D, iron, and B vitamins are common nutritional concerns during GLP-1 treatment and especially relevant with Hashimoto’s.

Evidence: MODERATE

Studies of people taking GLP-1 medications have reported deficiencies or inadequate intake of vitamin D, thiamine and other B vitamins, iron, calcium, magnesium, and potassium. [38] The main concern appears to be reduced food intake and dietary variety rather than proven malabsorption.

For someone with Hashimoto’s, a few deserve particular attention:

• Iron is required for normal thyroid hormone production, and emerging evidence suggests iron deficiency may occur in some GLP-1 users. [39]
• Vitamin B12 deficiency is already more common in people with autoimmune thyroid disease, partly because autoimmune gastritis and pernicious anemia can occur alongside Hashimoto’s. [40]
• Vitamin D deficiency is common in both obesity and autoimmune thyroid disease, although whether correcting it directly changes Hashimoto’s disease activity remains uncertain.
• Calcium and iron supplements can interfere with levothyroxine absorption if taken too close to the medication.
• Protein deficiency can impair thyroid hormone production, and it’s a common effect of GLP-1s due to the delayed gastric emptying and decreased food intake mentioned earlier

Selenium is also important for normal thyroid function and antioxidant protection, but current evidence does not suggest that selenium deficiency is a common problem specifically caused by GLP-1 treatment.

This does not mean everyone taking a GLP-1 needs supplements. The practical concern is making sure that a much smaller appetite still provides adequate nutrition, and discussing persistent symptoms or very restricted intake with your clinician.

15. Does losing fat quickly release stored chemicals into my blood?

Yes. Certain persistent, fat-soluble pollutants stored in body fat can be released back into the bloodstream during substantial weight loss. Whether this has meaningful thyroid effects is much less clear.

Evidence: STRONG that major weight loss can increase circulating levels of some persistent organic pollutants (POPs). LIMITED on the clinical consequences, including effects on thyroid function. No direct evidence yet for GLP-1–induced weight loss specifically.

Persistent organic pollutants—including some older pesticides, PCBs, and flame retardants—can accumulate in body fat and remain there for years. Studies of people undergoing major weight loss have consistently found that blood levels of several of these chemicals rise as fat mass decreases.[41], [42]

Some of these pollutants can interfere with thyroid hormone signaling, but whether their temporary increase during weight loss meaningfully affects thyroid function is uncertain. One bariatric-surgery study found associations between changes in certain pollutants and thyroid hormones, but it could not establish cause and effect.[43]

Nobody has studied this specifically during GLP-1–induced weight loss yet. The underlying physiology makes the same process plausible, but that remains an inference rather than demonstrated GLP-1 evidence.

Importantly, this is not evidence that losing weight is harmful. For people with obesity, the established health benefits of weight loss remain substantial. [41]

16. How do I tell whether a symptom is because of abnormal thyroid levels or the GLP-1?

Often, you can't tell from the symptom alone. There is a lot of overlap, but certain patterns can point more strongly in one direction.

Evidence: STRONG for the typical symptoms of thyroid dysfunction and common GLP-1 side effects. This table is an orientation aid, not a diagnostic tool.

Symptom	Suggestive of undertreated thyroid?	Suggestive of too much thyroid hormone?	Suggestive of the GLP-1 or rapid weight loss?
Constipation	Common	Less typical	Common
Nausea, feeling full quickly	Less typical	Less typical	Yes — very common
Fatigue / Brain fog	Common	Possible	Common — especially with low food intake or dehydration
Hair loss	Possible	Possible	Yes — can occur with rapid weight loss or inadequate nutrition
Feeling cold all the time	Common	Unlikely	Possible after large weight loss
Palpitations / racing heart	Less typical	**More concerning - get checked **	Can occur, but less characteristic
Anxiety, insomnia, tremor	Less typical	More concerning — get checked	Possible
Muscle weakness	Yes	Yes	Yes — muscle loss
Feeling hot, sweating	Unlikely	More concerning — get checked	Less typical

The challenging symptoms are the nonspecific ones—such as fatigue, brain fog, hair loss, weakness, and constipation—since thyroid issues, GLP-1 side effects, rapid weight loss, and poor nutrition can all play a role.[17], [44–46]

Symptoms serve as helpful signals but should not replace thyroid blood tests. If you experience new, persistent, or changing symptoms—such as palpitations, tremor, heat intolerance, or significant fatigue—especially during GLP-1 treatment, it’s important to discuss your thyroid levels with your clinician instead of assuming the GLP-1 or Hashimoto’s disease is the cause.

17. How often should my thyroid be rechecked?

There’s no official GLP-1-specific guideline yet, so this is something worth planning with your doctor.

Evidence: STRONG for standard thyroid monitoring after levothyroxine changes. [17] LIMITED on the ideal monitoring schedule specifically during GLP-1 treatment.

A sensible monitoring plan to discuss with your doctor might include:

• Check TSH around 6–8 weeks after starting a GLP-1, particularly if you take levothyroxine. [17]
• Recheck after GLP-1 or levothyroxine dose changes, especially if your weight is changing quickly.
• Consider rechecking after a meaningful change in body weight—for example, around 5–10%.
• Once your weight and thyroid levels are stable, return to your usual monitoring schedule.
• Check again if you stop the GLP-1, since weight regain or other metabolic changes could shift your thyroid hormone requirements again.

There is no single schedule that fits everyone. The main point is that your levothyroxine needs may change while your weight and metabolism are changing, so thyroid monitoring may need to be more frequent than usual during that period.

How to use this information

Take the checklist to your next appointment. Ask for a monitoring plan and get it written down. Learn the third column of that symptom table. And the next time an alarming headline about these drugs comes across your feed, ask who was studied, whether any other studies or cases found the same thing, and what the rest of the research says — before you let it change your mind.

Starting a GLP-1 while living with Hashimoto’s or hypothyroidism should be a high-information, thoughtful decision between you and your doctor. It’s important to understand the full picture of your disease and exposures before considering a GLP-1; reducing other external exposures could help address the thyroid issues and weight gain. At the very least, you should think about GLP-1s as one exposure among thousands that shapes your immune system and your thyroid — alongside past infections, chemicals, deficiencies, other medications, and places you've lived.

You don't need to become an expert in thyroid medicine. You need enough of the picture to ask good questions and to notice when an answer is thinner than it sounds. This is why we’ve added GLP-1s to EXPIN as an exposure for you to note, so it can be weighed alongside everything else in your history instead of sitting in a box by itself.

Map your exposures →

EXPIN is a research and educational tool for understanding what may be driving your condition. It is not a medical device, and it does not diagnose, treat, or cure disease. Nothing on this page is medical advice, and nothing here is a recommendation for or against any medication. Decisions about GLP-1 receptor agonists and thyroid hormone replacement should be made with your own clinician, who knows your history.

Last reviewed: August 31, 2026. This guide will be updated as new evidence emerges.

References

[1]: Chukir T, Yaghmour M, Almutairi T, Chagoury O, Taheri S. Weight and body composition outcomes with liraglutide in individuals with well-treated hypothyroidism: A retrospective case-control study. PLOS One. 2025;20(9):e0332091. doi:10.1371/journal.pone.0332091

[2]: Heymsfield SB, Thomas D, Nguyen AM, et al. Voluntary weight loss: systematic review of early phase body composition changes. Obesity Reviews. 2011;12(5):e348-e361. doi:10.1111/j.1467-789X.2010.00767.x

[3]: Laurens C, Grundler F, Damiot A, et al. Is muscle and protein loss relevant in long-term fasting in healthy men? A prospective trial on physiological adaptations. Journal of Cachexia, Sarcopenia and Muscle. 2021;12(6):1690-1703. doi:10.1002/jcsm.12766

[4]: Krotkiewski M, Toss L, Björntorp P, Holm G. Loss of total body potassium during rapid weight loss does not depend on the decrease of potassium concentration in muscles. Different methods to evaluate body composition during a low energy diet. International Journal of Obesity. 2000;24(1):101-107. doi:10.1038/sj.ijo.0801092

[5]: Misra S, et al. Does Bariatric Surgery Impact Hypothyroidism and Vice Versa? Results of a Prospective Comparative Study. Obesity Surgery. 2025. doi:10.1007/s11695-025-08109-8

[6]: Guan B, et al. Effect of Bariatric Surgery on Thyroid Function in Obese Patients: A Systematic Review and Meta-Analysis. Obesity Surgery. 2017. doi:10.1007/s11695-017-2965-2

[7] Al-Husni D, Flores M, Cheema AY, Munir M, Mandala A, Griebeler ML. Thyroid Trade-Offs: GLP-1 Receptor Agonists and Levothyroxine in Hypothyroidism: A Global Propensity Score-Matched Analysis. Presented at ENDO 2026; June 13, 2026. Abstract SAT-306.

Important: this is a conference abstract, not yet a full peer-reviewed publication. The matched analysis included 82,520 pairs and found significantly lower TSH among GLP-1 users.

[8] Yu GK, Nakhle S, Vernetti NJ, Chao A. Changes in Thyroid Function Test With Tirzepatide Use in Patients With Hypothyroidism. Journal of the Endocrine Society. 2023;7(Suppl 1):bvad114.1829. doi:10.1210/jendso/bvad114.1829.

Also an abstract-level publication; small retrospective series (n=17).

[9]: Juiz-Valiña P, et al. Central Resistance to Thyroid Hormones in Morbidly Obese Subjects Is Reversed after Bariatric Surgery-Induced Weight Loss. Journal of Clinical Medicine. 2020;9(2):359. doi:10.3390/jcm9020359

[10]: Biondi B. Subclinical Hypothyroidism in Patients with Obesity and Metabolic Syndrome: A Narrative Review. Nutrients. 2023;16(1):87. doi:10.3390/nu16010087

[11] Tee SA, Tsatlidis V, Razvi S. The GLP-1 receptor agonist exenatide reduces serum TSH by its effect on body weight in people with type 2 diabetes. Clinical Endocrinology. 2023;99(4):401–408. doi:10.1111/cen.14901.

[12] American Thyroid Association. Thyroid Function Tests. Accessed August 2026. This is our broader clinical reference for medication effects, estrogen/pregnancy, and biotin interference with thyroid-test interpretation.

[13] Ylli D, Soldin SJ, Stolze B, et al. Biotin Interference in Assays for Thyroid Hormones, Thyrotropin and Thyroglobulin. Thyroid. 2021;31(8):1160–1170. doi:10.1089/thy.2020.0866.

[14] Hauge C, Breitschaft A, Hartoft-Nielsen ML, Jensen S, Bækdal TA. 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. Expert Opinion on Drug Metabolism & Toxicology. 2021;17(9):1139–1148. doi:10.1080/17425255.2021.1955856.

[15] U.S. prescribing information / DailyMed. RYBELSUS and OZEMPIC tablets (semaglutide), for oral use. Updated 2026. The label states that levothyroxine exposure increased 33% when administered with oral semaglutide and recommends considering increased monitoring for oral medications requiring close clinical or laboratory follow-up.

[16] Wilcox L, Van Dril E. Suppressed thyroid stimulating hormone levels after initiation of a subcutaneous glucagon-like peptide-1 receptor agonist in a post-thyroidectomy patient managed with levothyroxine: case report. Journal of the American Pharmacists Association. 2024;64(6):102185. doi:10.1016/j.japh.2024.102185.

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[18] U.S. prescribing information / DailyMed. WEGOVY (semaglutide) injection and tablets. Updated June 2026. Used for the boxed warning, MTC/MEN2 contraindication, delayed gastric emptying/oral-drug considerations, and the FDA position that the human relevance of rodent C-cell tumors remains unknown.

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