Levothyroxine and Semaglutide: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Semaglutide
Levothyroxine
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Increased levothyroxine exposure, decreased TSH and worsening of glycemic control
Interaction Deep Dive
Concomitant administration of semaglutide and oral levothyroxine may result in increased levothyroxine exposure. Consider increased clinical or laboratory monitoring for medications that have a narrow therapeutic index (NTI) or that require clinical monitoring, such as levothyroxine. In a study, thyroxine AUC increased by 33% after administration of a single dose of levothyroxine 600 mcg concurrently with oral semaglutide. If using oral semaglutide, administer on an empty stomach at least 30 minutes before other oral medications4. Additionally, decreased weight-based levothyroxine dosages (about 25% to 30%) have been required in patients experiencing subacute hyperthyroidism or thyrotoxicosis following weight loss from semaglutide 25. In patients with diabetes mellitus, levothyroxine use may worsen glycemic control and result in increased antidiabetic agent or insulin requirements; monitor carefully after starting, changing, or discontinuing levothyroxine 1.
Why it happens (mechanism)
Delayed gastric emptying by semaglutide resulting in increased levothyroxine absorption; decreased weight-based levothyroxine requirements with weight loss
Literature reports
3 reports — tap to read
a) Thyrotoxicosis following rapid weight loss from semaglutide therapy was described in a case report involving a patient receiving a stable dose of levothyroxine. The patient was a female in her 50s with a history of hypothyroidism, obesity (current weight, 101.2 kg), and type 2 diabetes receiving levothyroxine 125 mcg daily, semaglutide 0.5 mg weekly and metformin 500 mg twice daily. She presented with symptoms of palpitations, perspiration, and heat intolerance. Significant findings on presentation included regular sinus tachycardia, an unmeasurable TSH (less than 0.005 milli-international units/L) and significant weight loss (17.7 kg in 5 months). Five months prior, she was initiated on semaglutide 0.25 mg weekly for obesity, which was increased to the current dose of 0.5 mg weekly one month later. At that time, her TSH was 1.02 milli-international units/L and free T4 was 1.53 nanograms/mL, and she was receiving the same dose of levothyroxine (125 mcg daily). Levothyroxine was decreased to 100 mcg daily and semaglutide was increased to 1 mg weekly. At follow up 4 months later (9 months after semaglutide initiation), thyrotoxicosis symptoms had resolved and she lost an additional 4.5 kg. TSH was improved yet still low (0.0391 milli-international units/L) and levothyroxine was decreased again to 88 mcg daily. Two months later, all symptoms had resolved. In this case, a 30% reduction in levothyroxine dose was required since semaglutide initiation 2.
b) In a case report, subacute hyperthyroidism occurred following initiation and titration of SUBQ semaglutide in a patient receiving a stable dose of levothyroxine for 5 years. The patient was a 43-year-old female with postoperative hypothyroidism following total thyroidectomy for papillary thyroid carcinoma, diabetes type 2, and obesity receiving semaglutide 1 mg weekly, levothyroxine 200 mcg orally daily (most recent TSH, 0.86 micro-international units/mL), metformin and insulin. A TSH of 0.01 micro-international units/mL and free T4 of 1 nanograms(ng)/dL were discovered on routine laboratory monitoring 13 months after semaglutide initiation and 8 months after achieving maximum approved dose; TSH had not been previously evaluated since semaglutide initiation. A weight loss of 10.5 kg occurred during this time. No symptoms related to abnormal TSH levels were noted. Levothyroxine was decreased to 175 mcg daily in response to low TSH. One month later, thyroid levels continued to reflect subacute hyperthyroidism (TSH, 0.05 micro-international units/mL; free T4, 1.1 ng/dL) and levothyroxine was further decreased to 150 mcg daily. TSH slowly returned to normal level over the next few months with no additional levothyroxine dose changes. No medication changes occurred from semaglutide initiation to the first abnormal TSH level that could cause drug interactions with either levothyroxine or semaglutide. A net weight loss of 14 kg occurred during the observation period. In this case, a 25% reduction in levothyroxine dose was required since semaglutide initiation 5.
c) Thyroxine AUC (adjusted for endogenous levels) was increased by 33% following administration of a single dose of levothyroxine 600 mcg concurrently administered with oral semaglutide. Cmax was unchanged 4.
Common questions
Can I take Levothyroxine and Semaglutide together?
Increased levothyroxine exposure, decreased TSH and worsening of glycemic control Always confirm with your pharmacist or prescriber before making any change.
How serious is the Levothyroxine and Semaglutide interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Levothyroxine or Semaglutide need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there anything you'd monitor while I'm on both?
References (5)
- Product Information: TIROSINT(R)-SOL oral solution, levothyroxine sodium oral solution. IBSA Pharma Inc. (per FDA), Parsippany, NJ, 2023. DailyMed
- Barnett MJL, Eidbo S, & Rivadeneira A: Semaglutide therapy and iatrogenic thyrotoxicosis. Endocrinol Diabetes Metab Case Rep 2025; 2025(3):e250065. PubMed
- Product Information: WEGOVY® subcutaneous injection, oral tablets, semaglutide subcutaneous injection, oral tablets. Novo Nordisk Inc (per FDA), Plainsboro, NJ, 2026. DailyMed
- Product Information: RYBELSUS(R) oral tablets, semaglutide oral tablets. Novo Nordisk Inc (per FDA), Plainsboro, NJ, 2023. DailyMed
- 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. J Am Pharm Assoc (2003) 2024; 64(6):102185. PubMed
Keep reading about Semaglutide
Keep reading about Levothyroxine
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