Most pages about tirzepatide side effects list symptoms without numbers. The Phase III record has numbers. In SURMOUNT-1, 33% of people on the top dose reported nausea, and roughly 4–7% stopped the drug because of an adverse event.
The short answer. Tirzepatide: In SURMOUNT-1's 15 mg arm, nausea was 33%, diarrhea 22%, vomiting 12%.
- Gut events were mostly mild to moderate and clustered during dose escalation.
- Roughly 4 to 7% of participants stopped tirzepatide because of an adverse event.
- Tirzepatide has no completed cardiovascular outcome trial; semaglutide's SELECT showed a 20% reduction in major events.
What are the most common tirzepatide side effects?
They are gastrointestinal, and they are common. Across the SURMOUNT program, gut side effects were reported by roughly 60–80% of participants depending on the dose and the event counted.
SURMOUNT-1 randomized 2,539 adults with obesity to 5, 10 or 15 mg once weekly, or placebo, for 72 weeks. The trial ran at 119 sites in 9 countries. Here is what the top-dose arm reported.
| Event | SURMOUNT-1, 15 mg arm |
|---|---|
| Nausea | 33% |
| Diarrhea | 22% |
| Vomiting | 12% |
| Discontinued for an adverse event | about 4–7% |
The most common adverse events with tirzepatide were gastrointestinal and were primarily mild to moderate in severity, occurring primarily during dose escalation.
Jastreboff et al., New England Journal of Medicine, 2022 (SURMOUNT-1)Two things sit inside that sentence. The events were mostly mild to moderate. And they clustered at a particular point in time, not evenly across the 72 weeks. The full trial write-up is in our SURMOUNT-1 page.
Why the escalation phase matters
Every arm in SURMOUNT-1 started at 2.5 mg. Steps up were 2.5 mg at a time, roughly every four weeks. Reaching 15 mg took about 20 weeks. That design is described in the dosage guide, which reports what the trials administered.
The reason the trials were built that way is the side-effect curve. Nausea and vomiting concentrated in the weeks when the amount was rising. That is reporting on trial design, not a schedule anyone should copy.
Side-effect rates in a trial are attached to that trial's supervised escalation. A number like 33% nausea does not transfer to a different amount, a different step size, or an unsupervized vial.
The head-to-head SURPASS-2 trial found the same pattern against semaglutide in type 2 diabetes: gut events were the most common adverse events in every arm, mostly mild to moderate, and mostly during escalation.
The most common adverse events were gastrointestinal and were primarily mild to moderate in severity, occurring primarily during the dose-escalation phase.
Frias et al., New England Journal of Medicine, 2021 (SURPASS-2)What the safety record does not contain
This is the part vendor pages skip. Tirzepatide has strong efficacy data and a well described gut profile. It does not yet have a completed cardiovascular outcome trial.
- No finished heart-outcome result. SURMOUNT-MMO is still open. SURPASS-CVOT results are pending.
- Semaglutide has that data and tirzepatide does not. In SELECT, semaglutide cut heart attacks, strokes and cardiovascular death by about 20% in people with obesity and no diabetes.
- Duration is bounded. SURMOUNT-1 measured 72 weeks. Obesity treatment is chronic. Years of exposure are not in the published set.
- Entry criteria were narrow. SURMOUNT-1 required a BMI of 30 or more, or 27 with a weight-related illness. People outside that band were not measured.
- Rare events need bigger numbers. A 2,539-person trial can characterize a 5% event well. It cannot rule out a 1-in-5,000 one.
Prescribing labels for the approved products also carry a boxed warning about thyroid C-cell tumors seen in rodents. Whether that finding translates to humans is not settled. We compare the two compounds' evidence bases in tirzepatide vs semaglutide.
Tirzepatide
The compound discussed here, supplied as a research compound with a certificate of analysis matched to the lot.
Is weight regain after stopping a side effect?
It is not an adverse event in the regulatory sense. It is still the most predictable thing that happens after discontinuation, and SURMOUNT-4 measured it.
That trial ran a lead-in on tirzepatide, then randomized 1,879 adults to continue or switch to placebo. Continuers reached 25.3% total weight reduction. The placebo group regained.
Withdrawing tirzepatide led to substantial regain of lost weight, whereas continued treatment maintained and augmented initial weight reduction.
Aronne et al., JAMA, 2024 (SURMOUNT-4)So the practical reading is that the 22.5% figure from SURMOUNT-1 is a figure for people still taking the drug. A 2024 review in the International Journal of Obesity places tirzepatide inside a wide pipeline of incretin agents, most of which share the same gut profile and the same open question about long-term exposure.
Do these numbers apply to a research vial?
No, and that gap runs in both directions. The trial safety profile was generated with a pharmaceutical-grade product, a fixed escalation, clinic monitoring and lab work. A gray-market vial has none of that attached to it.
- Identity and purity are unverified without a batch-specific certificate of analysis. See how to read a COA.
- Handling changes the material. Lyophilized peptide has storage requirements. See peptide storage temperature.
- The legal status is separate from the drug's approval status. A tirzepatide-labeled research vial is not Mounjaro or Zepbound. See are peptides legal.
The mechanism behind both the effect and the gut symptoms is covered in the dual agonist mechanism page. The 39-amino-acid peptide hits GIP and GLP-1 receptors at once, and slowed gastric emptying is part of how it works.
Tirzepatide
Research-use-only material, sold by the vial with batch documentation. Check the certificate of analysis against the batch you receive.
What to know now
- In SURMOUNT-1's 15 mg arm, nausea was 33%, diarrhea 22%, vomiting 12%.
- Gut events were mostly mild to moderate and clustered during dose escalation.
- Roughly 4 to 7% of participants stopped tirzepatide because of an adverse event.
- Tirzepatide has no completed cardiovascular outcome trial; semaglutide's SELECT showed a 20% reduction in major events.
- SURMOUNT-4 found substantial weight regain after withdrawal, so the trial figures describe ongoing treatment.
- Trial safety numbers belong to the supervised trial drug, not to an unverified research vial.
What we're watching
Tirzepatide side effects: what SURMOUNT-1 actually reported
Frequently asked questions
What percentage of people get side effects on tirzepatide?
Across the SURMOUNT program, gastrointestinal side effects were reported by roughly 60 to 80% of participants, depending on dose and which event is counted. In SURMOUNT-1's 15 mg arm, nausea was 33%, diarrhea 22% and vomiting 12%. Most were graded mild to moderate.
How long do tirzepatide side effects last?
The published trials do not give a duration per person. What they report is timing: in both SURMOUNT-1 and SURPASS-2, gastrointestinal events occurred primarily during the dose-escalation phase rather than spread evenly across the study.
Are tirzepatide side effects worse than semaglutide's?
SURPASS-2 compared them directly in type 2 diabetes. Gut events were the most common adverse events in every arm of that trial, tirzepatide and semaglutide alike, and were mostly mild to moderate. Tirzepatide produced more weight loss in that comparison, about 11.2 kg versus 5.7 kg.
Does tirzepatide have heart risks?
That question is not answered yet. SURMOUNT-MMO and SURPASS-CVOT, the cardiovascular outcome trials, have not reported. Semaglutide's SELECT trial showed about a 20% reduction in heart attack, stroke and cardiovascular death, but that result belongs to semaglutide.
What are the serious side effects the trials could not measure?
Anything rare. A trial of 2,539 people over 72 weeks characterizes common events well and cannot exclude events that occur once in several thousand exposures. The approved product labels also carry a boxed warning about thyroid C-cell tumors observed in rodents, whose relevance to humans is unresolved.
Do research-grade vials carry the same side-effect profile?
There is no dataset that says so. Every number on this page came from a supervised trial using pharmaceutical-grade product with monitoring and lab work. A vial without a batch-specific certificate of analysis has unverified identity and purity.
References
- Jastreboff, A. M., Aronne, L. J., Ahmad, N. N., et al. (2022). Tirzepatide once weekly for the treatment of obesity. New England Journal of Medicine, 387(3), 205–216. https://doi.org/10.1056/NEJMoa2206038
- Aronne, L. J., Sattar, N., Horn, D. B., et al. (2024). Continued treatment with tirzepatide for maintenance of weight reduction in adults with obesity: The SURMOUNT-4 randomized clinical trial. JAMA, 331(1), 38–48. https://doi.org/10.1001/jama.2023.24945
- Frias, J. P., Davies, M. J., Rosenstock, J., et al. (2021). Tirzepatide versus semaglutide once weekly in patients with type 2 diabetes. New England Journal of Medicine, 385(6), 503–515. https://doi.org/10.1056/NEJMoa2107519
- Lincoff, A. M., Brown-Frandsen, K., Colhoun, H. M., et al. (2023). Semaglutide and cardiovascular outcomes in obesity without diabetes. New England Journal of Medicine, 389(24), 2221–2232. https://doi.org/10.1056/NEJMoa2307563
- Wilding, J. P. H., Batterham, R. L., Calanna, S., et al. (2021). Once-weekly semaglutide in adults with overweight or obesity (STEP-1). New England Journal of Medicine, 384(11), 989–1002. https://doi.org/10.1056/NEJMoa2032183
- Melson, E., Ashraf, U., Papamargaritis, D., & Davies, M. J. (2024). What is the pipeline for future medications for obesity? International Journal of Obesity, 49(3), 433–451. https://doi.org/10.1038/s41366-024-01473-y