# Do GLP-1 Drugs Cause Blood Clots? No Untreated Group Was Ever Followed A 701,374-person cohort put venous thromboembolism at HR 0.90 on tirzepatide against other GLP-1 drugs | negative controls and E-values tested how fragile that result is. Publisher: This GLP Editorial Team Canonical: https://thisglp.com/research/do-glp1-drugs-cause-blood-clots Updated: 2026-09-17 Published: 2026-09-17 [← Research](https://thisglp.com/research) Evidence # Do GLP-1 Drugs Cause Blood Clots? No Untreated Group Was Ever Followed Every published comparison ranks one of these drugs against another, never against taking nothing. The effect is small, the method is unusually careful, and the lung clots moved while the leg clots did not. [This GLP Editorial Team](https://thisglp.com/about)September 20268 min read Tirzepatide vs other GLP-1 drugs, 1 year · blood clots overall · 0.90 · pulmonary embolism · 0.88 · deep vein thrombosis · 0.96 · death, any cause · 0.90 · Clots in the lung moved. Clots in the leg did not. **Research, not medical advice.** This GLP is independent and educational. Nothing here is a substitute for individualized care from a licensed clinician, and reading it creates no doctor–patient relationship. Talk to your own provider before starting, stopping, or changing any medication, peptide, or therapy. See our [methodology](https://thisglp.com/methodology) and [terms](https://thisglp.com/terms). ## Key takeaways - A cohort of 701,374 matched adults with obesity compared tirzepatide against other GLP-1 drugs for blood clots over one year. - Venous thromboembolism came in at a hazard ratio of 0.90 (95% CI 0.83-0.98), driven by pulmonary embolism (0.88) and accompanied by lower all-cause mortality (0.90). - Deep vein thrombosis showed no difference (0.96, 95% CI 0.86-1.07) — awkward, since most pulmonary emboli begin as leg clots. - The study used negative control outcomes and E-values to test its own vulnerability to confounding. No large study has compared GLP-1 users against untreated people for clots, so the honest answer is that nobody has measured it. The one big comparison that exists ranks two of these drugs against each other rather than against nothing. In 701,374 matched adults with obesity, venous thromboembolism over one year came in at a hazard ratio of 0.90 (95% CI 0.83 to 0.98) on tirzepatide against other GLP-1 drugs [\[1\]](https://thisglp.com/research/do-glp1-drugs-cause-blood-clots#ref-1). Most claims studies report an association and leave the reader to guess how much unmeasured confounding would erase it, and this one tests that directly, which makes it worth reading for its method as much as its result. Other comparisons between the same two drugs are in [the semaglutide and tirzepatide comparison](https://thisglp.com/research/bigger-relative-smaller-absolute). Two instruments were used. A negative control outcome is something the drug could not plausibly affect: if the analysis finds an effect there, the method is manufacturing associations. An E-value asks how strong an unmeasured confounder would have to be, in association with both treatment and outcome, to explain away the result entirely. Together they convert “this might be confounded” from an objection into a quantity. The finding itself is modest. Venous thromboembolism over one year gave a hazard ratio of 0.90 with a confidence interval of 0.83 to 0.98. An upper bound that close to 1 across 701,374 people describes a small effect measured precisely — the precision comes from the sample size, not from the size of the difference. The lung clots moved and the leg clots did not Pulmonary embolism came in at 0.88 and deep vein thrombosis at 0.96, with an interval crossing no effect. The overwhelming majority of pulmonary emboli begin as deep vein thromboses that travel, so a treatment reducing the destination without reducing the origin is mechanistically awkward. That pattern is a reason for caution the abstract does not draw, and it is the kind of internal inconsistency worth more than the headline. A separate target trial emulation set semaglutide against tirzepatide on cardiovascular and cerebrovascular outcomes rather than clots [\[2\]](https://thisglp.com/research/do-glp1-drugs-cause-blood-clots#ref-2). Between them the two studies make the same shape of claim. One of these drugs edges the other by a margin small enough that the choice of comparator and the coding of the records matter as much as the molecules do. Neither has an untreated arm, so neither can tell a reader whether taking a GLP-1 at all raises or lowers the chance of a clot. All-cause mortality also fell, at 0.90 — the same magnitude as the primary outcome. In a one-year study of blood clots, a mortality difference of equal size suggests the two arms differ in general health rather than specifically in clotting risk. That is the pattern described at greater length in [six unrelated complications all halved](https://thisglp.com/research/when-a-drug-improves-everything). That the authors ran negative controls makes this less likely than it otherwise would be, without eliminating it. For a reader the practical content is small and the methodological content is not. A 10% relative reduction in clots between two drugs in the same class is not a reason to choose between them. It sits alongside the other small tirzepatide advantages this site has covered in [the glaucoma comparison](https://thisglp.com/research/do-glp1-drugs-cause-glaucoma) and [the carpal tunnel cohort](https://thisglp.com/research/do-glp1-drugs-help-carpal-tunnel-syndrome). What is genuinely useful is that a large claims study can quantify its own fragility, and that most do not. ## Frequently asked Is tirzepatide safer than other GLP-1 drugs for blood clots? The hazard ratio was 0.90 with an upper bound of 0.98 — a small difference measured precisely in 701,374 people. It is not large enough to drive a choice between the two. What is an E-value? A measure of how strong an unmeasured confounder would have to be, in its association with both the treatment and the outcome, to fully explain away a reported result. Why does the deep vein thrombosis result matter? Most pulmonary emboli begin as deep vein thromboses. A treatment that reduces lung clots without reducing leg clots is mechanistically difficult to explain, which is a reason for caution. ## Sources 1. \[1\] Wu JY, Lee KW, Huang SC, Chang HY, Lin YM (2026). Comparative effectiveness of tirzepatide versus GLP-1 receptor agonists on the risk of venous thromboembolism in patients with obesity: a real-world cohort study Frontiers in Medicine. [PMID 42239959](https://pubmed.ncbi.nlm.nih.gov/42239959/) 2. \[2\] Azzam AY, Essibayi MA, Rai P, Salim HA, et al. (2026). Cardiovascular and Cerebrovascular Outcomes Risk Reduction Associated With Semaglutide vs Tirzepatide: A Target Trial Emulation JACC: Advances. [PMID 42489387](https://pubmed.ncbi.nlm.nih.gov/42489387/) ## Where to get it ### Best GLP-1 injections Every injectable seller we can verify, with the price each one publishes and an honest read of what the trials measured. 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