- In the semaglutide STEP 1–3 trials, 43.9% of people on semaglutide 2.4 mg reported nausea at some point, compared with 16.1% on placebo.1
- Stomach side effects were mostly mild to moderate, clustered around dose increases, and a typical nausea episode lasted about 8 days.1
- Few people stopped treatment because of them: 4.3% on semaglutide in STEP 1–3. Weight loss was about the same whether or not people felt sick.1,3
How often it happens
The clearest numbers for semaglutide come from a pooled analysis of the STEP 1, 2 and 3 trials: 2,117 adults on semaglutide 2.4 mg and 1,262 on placebo, all with overweight or obesity, followed for 68 weeks. STEP 1 and 3 excluded people with diabetes; STEP 2 enrolled people with type 2 diabetes.1
Overall, 72.9% of people on semaglutide reported at least one stomach or bowel side effect, but so did 47.1% on placebo. The authors note that obesity itself carries a higher background rate of these complaints.1
Tirzepatide looks similar. In SURMOUNT-3, adults without diabetes who had already lost at least 5% with a lifestyle program were randomized to tirzepatide (10 or 15 mg) or placebo for 72 weeks.5
| Tirzepatide (n = 287) | Placebo (n = 292) | |
|---|---|---|
| Nausea | 39.7% | 14.0% |
| Diarrhea | 31.0% | 9.2% |
| Constipation | 23.0% | 6.8% |
| Vomiting | 18.1% | 1.4% |
Across the four SURMOUNT-1 to -4 trials, 27.8% to 72.8% of people on tirzepatide reported at least one stomach or bowel side effect, vs 12.2% to 32.5% on placebo.3 Comparing rates between separate trials is tricky, because the populations and placebo rates differ. For a direct comparison, see semaglutide vs tirzepatide.
When it happens, and how long it lasts
In both drug programs, side effects bunched up during the dose-escalation period, while the dose is being stepped up. In the STEP trials that meant a step every four weeks until the full dose at week 16; the SURMOUNT trials used a 20-week escalation.1,3 In STEP 1–3, the share of people with nausea, diarrhea or vomiting peaked around week 20 and fell after that. Nausea showed the biggest drop.1
Individual episodes of nausea, diarrhea and vomiting were short, and similar in length to placebo. Constipation was the exception: it tended to last for weeks.1
How serious it got
In STEP 1–3, 99.5% of stomach side effects were non-serious and 98.1% were mild or moderate. Severe events were reported by 4.1% of people on semaglutide vs 0.9% on placebo.1 In SURMOUNT-1 to -4, severe or serious stomach events occurred in 0.3% to 5.6% of participants.3
Most people stayed on treatment:
- Semaglutide, STEP 1–3: 12.5% had a dose lowered or paused because of stomach symptoms, and 4.3% stopped for good (vs 0.7% on placebo).1 In STEP 1 alone, 4.5% stopped for stomach reasons vs 0.8% on placebo.2
- Tirzepatide, SURMOUNT-1: 4.3%, 7.1% and 6.2% on the 5, 10 and 15 mg doses stopped because of any side effect, vs 2.6% on placebo.4 Across SURMOUNT-1 to -4, 1.0% to 10.5% stopped because of stomach side effects.3
What helped in the trials and in clinical guidance
In the SURMOUNT trials, people with hard-to-tolerate symptoms were first counseled on diet: eat smaller meals, split three meals into four or more, and stop eating when full. If that was not enough, doctors could prescribe anti-nausea or anti-diarrhea medicine, pause one dose, or lower the dose.3 Between 13.8% and 27.5% of people on tirzepatide used an anti-nausea medicine at some point, mostly early on.3
A 2025 joint advisory from four US nutrition and obesity societies adds practical points:6
- Don't go long without food. Nausea often shows up in the morning or after long gaps. Some people get stuck in a loop where nausea stops them eating, which makes nausea worse. The advisory suggests a small breakfast, then small meals every 3–4 hours, with enough fluids.
- Go easy on fatty and high-fiber foods in the first few days of treatment. Large meals make vomiting more likely.
- Try gentle extras. Ginger or peppermint tea and acupressure bands may help some people.
- Get ahead of constipation. Drink enough, and add fiber gradually, for example prunes or other dried fruit. Foods high in fat or protein slow the stomach further and can make constipation worse.
- Watch for dehydration. Severe nausea, vomiting or diarrhea can dehydrate you, and the advisory notes this can cause acute kidney injury. Contact your care team if you cannot keep fluids down.
Protein still matters while appetite is low. See how much protein the research suggests. Any change to your dose or the pace of increases is a decision for you and your prescriber, not something to adjust alone.
Sources
- Wharton S, Calanna S, Davies M, et al. Gastrointestinal tolerability of once-weekly semaglutide 2.4 mg in adults with overweight or obesity, and the relationship between gastrointestinal adverse events and weight loss. Diabetes Obes Metab. 2022;24(1):94-105. PubMed · Full text (PMC)
- Wilding JPH, Batterham RL, Calanna S, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). N Engl J Med. 2021;384(11):989-1002. PubMed
- Rubino DM, Pedersen SD, Connery L, et al. Gastrointestinal tolerability and weight reduction associated with tirzepatide in adults with obesity or overweight with and without type 2 diabetes in the SURMOUNT-1 to -4 trials. Diabetes Obes Metab. 2025;27(4):1826-1835. PubMed · Full text (PMC)
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med. 2022;387(3):205-216. PubMed
- Wadden TA, Chao AM, Machineni S, et al. Tirzepatide after intensive lifestyle intervention in adults with overweight or obesity: the SURMOUNT-3 phase 3 trial. Nat Med. 2023;29(11):2909-2918. PubMed · Full text (PMC)
- Mozaffarian D, Agarwal M, Aggarwal M, et al. Nutritional priorities to support GLP-1 therapy for obesity: A joint Advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association, and The Obesity Society. Obesity (Silver Spring). 2025;33(8):1475-1503. PubMed · Full text (PMC)
