What are the side effects of tirzepatide?
FAQGastrointestinal effects dominate, as across the incretin class, and were most pronounced during dose escalation. Nausea was reported in 18–33% of trial participants at peak doses and diarrhoea in 12–23%. In the one head-to-head trial, discontinuation for gastrointestinal effects was 2.7% with tirzepatide against 5.6% with semaglutide.
Reported rates
| Effect | Reported rate | Reported in |
|---|---|---|
| Nausea | 18–33% | SURPASS / SURMOUNT, peak doses |
| Diarrhoea | 12–23% | SURPASS / SURMOUNT |
| Constipation | 6–17% | SURPASS / SURMOUNT |
| Vomiting | 8–13% | SURPASS / SURMOUNT |
| Discontinuation for GI effects | 2.7% | SURMOUNT-5 (head-to-head) |
Every figure here is an observed rate in a controlled trial population, not a prediction for any individual. Injection-site reactions, fatigue in the 48–72 hours after administration, and transient liver-enzyme elevations were also reported, at rates the published summaries do not consistently quantify.
The comparative figure, and its limits
SURMOUNT-5 is the reason a tirzepatide-versus-semaglutide tolerability comparison can be made at all: both arms were randomised within one study, so the 2.7% against 5.6% discontinuation figure is not an artefact of different populations. What it does not establish is a general tolerability ranking. It measured discontinuation in one trial at one pair of dose ceilings, and the compounds’ escalation ladders differ in both length and step size, which is itself a plausible contributor.
The boxed warning, stated precisely
The approved labels carry a boxed warning regarding thyroid C-cell tumours, drawn from rodent studies rather than from human trial findings. Human relevance was not determined by those studies, and the human trials were neither designed nor powered to resolve it. It is therefore neither a reported rate nor a refutation — it is an unresolved animal signal that the labels disclose, and reporting it as either a demonstrated human risk or a dismissed one misstates it in opposite directions.
What this data does not cover
These rates come from controlled trials of an approved, inspected product administered at defined doses under supervision. A vial bought on the research market is not that product, and the safety profile does not transfer to it: identity, purity and actual content are separate questions from pharmacology, and no rate table can speak to them.
For other common questions regarding tirzepatide, see the full Tirzepatide profile.
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