# GLP-1s and Autoimmune Thyroiditis: An Association, and the Reason to Doubt It By Ruth Calder, Enforcement Editor (https://glpwatchdog.org/authors/ruth-calder) | Published: 2026-08-31 | Updated: 2026-10-27 Canonical page: https://glpwatchdog.org/research/glp1-and-autoimmune-thyroiditis > A 290,770-pair cohort found autoimmune thyroiditis diagnosed 30% more often on a GLP-1 than on a DPP-4 inhibitor. Everyone on a GLP-1 gets a boxed thyroid warning and the comparison group does not, and this disease is found by testing. ## Key points - Autoimmune thyroiditis hazard ratio 1.30 (95% CI 1.24–1.38) vs DPP-4 inhibitors, across 290,770 matched patients per arm over eight years. - Detection bias is the likeliest explanation: a boxed thyroid warning prompts testing in one arm only, and this disease is diagnosed by test rather than by symptoms. - The same cohort found psoriasis 1.17, ankylosing spondylitis 1.30, ulcerative colitis 1.11 and rheumatoid arthritis 1.08, where that bias is weaker. - This is NOT the medullary thyroid carcinoma boxed warning. Different disease, different evidence. A very large cohort study found people taking a GLP-1 were diagnosed with autoimmune thyroiditis about 30% more often than people taking a comparable diabetes drug. The number is real and the study is a serious one. The likeliest explanation, though, is not the drug itself but the label that comes with it. Everyone taking these drugs is handed a warning about their thyroid, and warnings produce tests. ## What was measured Researchers took a US medical-records network covering 4.8 million adults with type 2 diabetes, identified 412,021 people starting a GLP-1 receptor agonist and 383,415 starting a DPP-4 inhibitor between 2015 and 2022, and matched them on baseline characteristics to 290,770 in each arm. Followed for up to eight years, the GLP-1 group had a higher recorded incidence of several autoimmune conditions: autoimmune thyroiditis at a hazard ratio of 1.30 (95% CI 1.24–1.38), ankylosing spondylitis also 1.30, psoriasis 1.17, [ulcerative colitis](https://glpwatchdog.org/research/glp1-and-inflammatory-bowel-disease) 1.11 and [rheumatoid arthritis](https://glpwatchdog.org/research/glp1-and-rheumatoid-arthritis) 1.08. Sensitivity analyses held.[1] Those are narrow confidence intervals on very large numbers, which is what makes the association hard to dismiss as noise. But what the study counted is how often a diagnosis was *recorded*, which is not the same thing as how often the disease occurred. ## The comparison group is the problem > Every person starting a GLP-1 receives a boxed warning about thyroid tumors. Nobody starting a DPP-4 inhibitor receives anything like it. So one arm of this study was systematically prompted toward thyroid attention and the other was not. Autoimmune thyroiditis is a condition that is found by testing rather than by symptoms severe enough to force the issue. That is textbook detection bias, and it produces exactly this shape of result: a moderate, statistically solid elevation in a diagnosis that requires somebody to order a test. The study is an active-comparator new-user design, which is the right way to build it and handles a great deal of confounding. It cannot handle this one, because the exposure itself changes the probability of being looked at. The authors present an association and recommend monitoring; they do not claim causation, and neither should anyone quoting them. Detection bias is the likeliest explanation, but it is not the only one. GLP-1 receptors appear on immune cells and the drugs have measurable immunomodulatory effects, so a real mechanism is not far-fetched. What is missing is any study designed to tell the two apart, one in which both groups get the same thyroid testing schedule regardless of which drug they are on. ## The second study, and why its number should not be quoted A 2026 chart review followed 527 patients through twelve months of tirzepatide at 2.5 to 15 mg weekly. Twenty-eight of them (5.3%) developed or had progression of some thyroid condition, most often nodular or goiter disease and drug-induced thyroiditis. On multivariate analysis, two things predicted it: end-stage renal disease, at an odds ratio of 2.94, and already having thyroid disease at baseline, at 3.78.[2] > That study has no comparison group. Its 5.3% over a year has nothing to be 5.3% *more or less than*: no untreated arm, no other drug, no background rate. And its strongest predictor is prior thyroid disease, which makes a good part of the finding “people with thyroid problems go on to have thyroid problems”. The study is useful for the one thing its authors propose, which is identifying who is worth watching. Someone starting tirzepatide who already has a thyroid diagnosis, or end-stage renal disease, is in a higher-risk group than someone who does not, and periodic thyroid testing in those two groups is a modest, cheap suggestion. It tells you whom to monitor, not how large the risk is. ## This is not the boxed warning Autoimmune thyroiditis and medullary thyroid carcinoma get confused constantly, and they have almost nothing to do with each other. The boxed warning on these labels concerns a thyroid *cancer* seen in rodents, and what it means for humans is covered separately in [what the thyroid cancer boxed warning says](https://glpwatchdog.org/research/glp1-thyroid-cancer-risk). Hashimoto’s and drug-induced thyroiditis are immune conditions, usually managed with thyroid hormone replacement, and nothing above about thyroiditis bears on cancer risk in either direction. The practical read is narrow. If you already have a thyroid condition, your prescriber should know before you start, and the second study is a reasonable argument for checking your thyroid function periodically once you have. If you do not, an association of this size, in a cohort that could not control for who got tested, is not a reason to change anything. ## Frequently asked questions ### Do GLP-1 drugs cause Hashimoto's thyroiditis? No study has shown that they cause it. A large US cohort found autoimmune thyroiditis diagnosed about 30% more often in GLP-1 users than in people taking DPP-4 inhibitors (hazard ratio 1.30, 95% CI 1.24-1.38, across 290,770 matched patients per arm). That is an association in medical records. Everyone starting a GLP-1 gets a boxed thyroid warning and the comparison group does not, so the GLP-1 arm is far more likely to have been tested. Autoimmune thyroiditis is found by testing. ### Is this the same as the thyroid cancer warning? No. The boxed warning on these labels concerns medullary thyroid carcinoma, a cancer seen in rodent studies. Autoimmune thyroiditis is an immune condition usually managed with thyroid hormone replacement. Different disease, different evidence, and nothing in the autoimmune data speaks to cancer risk either way. ### What other autoimmune conditions came up in that study? The same cohort reported higher recorded incidence of ankylosing spondylitis (hazard ratio 1.30), psoriasis (1.17), ulcerative colitis (1.11) and rheumatoid arthritis (1.08) alongside autoimmune thyroiditis at 1.30. The detection-bias problem is weaker for those, since a thyroid warning does not prompt testing for psoriasis. That is a reason to take the overall signal more seriously than the thyroid number alone. ### Should I have my thyroid checked while on a GLP-1? That is a question for your prescriber, and the answer depends on where you start. The one study that looked for risk factors found the two that mattered were already having thyroid disease (odds ratio 3.78) and end-stage renal disease (2.94); its authors suggested periodic thyroid testing for those groups specifically. It had no comparison group, so it cannot tell you how much risk that represents, only who is worth watching. ### How strong is this evidence overall? There are two studies. One is very large and well designed for everything except the thing that matters most here, namely who got tested. The other is a 527-patient chart review with no control group. Neither was built to establish cause. What would settle it is a study where both groups receive the same thyroid testing schedule regardless of which drug they take, and no such study exists. ## References 1. Lee YJ, Fang YW, Chen MT, et al. Association between autoimmune diseases and glucagon-like peptide-1 receptor agonists: A real-world evidence study. Journal of Autoimmunity. 2025. PMID: 40544585. https://pubmed.ncbi.nlm.nih.gov/40544585/ 2. Manueli Laos EG, Serafica B, Fontaine-Nicola A, et al. Impact of Tirzepatide Therapy on Thyroid Disease: Understanding Risks and Emerging Insights. Clinical Obesity. 2026. PMID: 42145153. https://pubmed.ncbi.nlm.nih.gov/42145153/ --- Cite as: GLP Watchdog, Ruth Calder, "GLP-1s and Autoimmune Thyroiditis: An Association, and the Reason to Doubt It", published 2026-08-31, updated 2026-10-27. https://glpwatchdog.org/research/glp1-and-autoimmune-thyroiditis Canonical HTML page: https://glpwatchdog.org/research/glp1-and-autoimmune-thyroiditis Medical disclaimer: Nothing here is medical advice. We report on this subject; we do not treat anyone. Whether to begin a medication, supplement, or treatment, whether to adjust it, and whether to stop are questions for a clinician licensed to answer them, who knows your history.