Semaglutide therapy and iatrogenic thyrotoxicosis.

Barnett MJL, Eidbo S, Rivadeneira A

Endocrinology, diabetes & metabolism case reports10 Jul 2025

PMID40638337PMCIDPMC12260150DOI10.1530/edm-25-0065PepBankPUB-40638337

Summary

SummaryLevothyroxine is the backbone of hypothyroidism treatment. The dosage of levothyroxine varies; however, as an estimate, an average adult patient will require 1.6 micrograms per kilogram of body weight. We present the case of a patient with hypothyroidism, controlled on a stable dosage of levothyroxine, who subsequently began semaglutide therapy for obesity. She developed rapid weight loss and presented with palpitations as her main symptoms. Both clinical and biochemical analyses demonstrated new hyperthyroidism. With the weight loss, it was deemed that her levothyroxine dosage was no longer appropriate for her new weight and was over-suppressing her thyroid function (iatrogenic hyperthyroidism), requiring a dosage reduction. With follow-up, both clinical assessment and biochemical studies noted a reduction in the suppression of the thyroid axis. This case highlights the importance of considering a dosage reduction of levothyroxine when patients lose significant weight (such as with concurrent obesity medications), to prevent iatrogenic hyperthyroidism.Learning pointsWeight loss (pharmacological or surgical) can be associated with a reduction in TSH; it is unclear whether this is directly related to the reduction in body mass index. Hypothyroid patients on levothyroxine who are treated for obesity should be monitored for clinical and biochemical evidence of hyperthyroidism, and clinicians should anticipate that a dosage reduction may be required. The mechanism leading to iatrogenic hyperthyroidism in hypothyroid patients with weight loss therapy is unknown but believed to occur either from increased absorption of the medication or as a result of the weight loss itself (posing a supratherapeutic level of levothyroxine).

CC BYText from Europe PMC. Highlighted sentences are the source of results.

Results from this study3

3 results from studies that gave the peptide. 3 results from people.

01HumanCase report or seriesEfficacy outcome
In one woman with hypothyroidism on stable levothyroxine, semaglutide for obesity was followed by rapid weight loss.
In plain wordsIn one woman with an underactive thyroid, semaglutide for obesity was followed by rapid weight loss.
Peptide
Semaglutide
Outcome
DecreaseWeight loss
Study
n = 1
Outcome group
Body weight · Metabolic and weight
Studied dose
Dose not stated
Source sentences
Summary
She developed rapid weight loss
1 context sentence(design, population, supporting numbers)
Summary · context
We present the case of a patient with hypothyroidism, controlled on a stable dosage of levothyroxine, who subsequently began semaglutide therapy for obesity.
Show in the study text Report a problemFND-4063833701
02HumanCase report or seriesSafety outcome
In one woman with hypothyroidism on stable levothyroxine, palpitations appeared after semaglutide was started.
In plain wordsIn one woman with an underactive thyroid, palpitations appeared after she started semaglutide.
Peptide
Semaglutide
Outcome
IncreasePalpitations
Study
n = 1
Outcome group
Adverse events · Cardiovascular
Studied dose
Dose not stated
Source sentences
Summary
presented with palpitations as her main symptoms.
1 context sentence(design, population, supporting numbers)
Summary · context
We present the case of a patient with hypothyroidism, controlled on a stable dosage of levothyroxine, who subsequently began semaglutide therapy for obesity.
Show in the study text Report a problemFND-4063833702
03HumanCase report or seriesSafety outcome
In one woman with hypothyroidism on stable levothyroxine, new hyperthyroidism appeared after semaglutide-associated weight loss, which needed a levothyroxine dose reduction.
In plain wordsIn one woman, new overactive thyroid signs appeared after semaglutide-linked weight loss, and her thyroid tablet dose had to be lowered.
Peptide
Semaglutide
Outcome
IncreaseNew hyperthyroidism (iatrogenic) on unchanged levothyroxine
Study
n = 1
Outcome group
Adverse events · Endocrine and hormones
Studied dose
Dose not stated
Source sentences
Summary
Both clinical and biochemical analyses demonstrated new hyperthyroidism.
2 context sentences(design, population, supporting numbers)
Summary · context
With the weight loss, it was deemed that her levothyroxine dosage was no longer appropriate for her new weight and was over-suppressing her thyroid function (iatrogenic hyperthyroidism), requiring a dosage reduction.
Summary · context
We present the case of a patient with hypothyroidism, controlled on a stable dosage of levothyroxine, who subsequently began semaglutide therapy for obesity.
Show in the study text Report a problemFND-4063833703

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Version history

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Version 2Current
11 Oct 2026, 00:04 UTC
Study results updated
Version 1
9 Oct 2026, 03:06 UTC
First added · source update from Europe PMC

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