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GLP-1 side effects: nausea, constipation and what helps
Nausea, constipation and an upset stomach are the most talked-about parts of starting a GLP-1 medicine. Here's how common they are, when they tend to show up, and what expert advice suggests.
The short answer: Stomach side effects are common on GLP-1 medicines. In a large trial, 74% of people on the medicine reported them, vs 48% on placebo. They were typically mild to moderate and eased with time, and they're most often reported while the dose is being raised. Expert advice suggests smaller meals, going easy on fatty food at first, and enough fluids.
How common are GLP-1 side effects?
In the STEP 1 trial (1,961 adults, 68 weeks):
| GLP-1 medicine | Placebo | |
|---|---|---|
| Reported stomach or gut side effects | 74% | 48% |
| Stopped treatment because of stomach or gut side effects | 4.5% | 0.8% |
Nausea and diarrhea were the most common, followed by vomiting and constipation. The trial reports they were typically short-lived, mild to moderate, and eased with time. So most people had some, and most kept going.
When do GLP-1 side effects happen?
The FDA label says stomach side effects were most often reported while the dose was being raised. That's one reason doses go up step by step. A 2022 expert panel of doctors and diabetes nurses built its advice around exactly this stage: reaching the maintenance dose while keeping side effects manageable.
Some people also notice a pattern within their week, like feeling it more in the day or two after a shot. Logging how you feel shows you your own pattern.
What helps GLP-1 nausea?
The 2025 joint advisory from four nutrition and obesity groups (ACLM, ASN, OMA and TOS) suggests:
- Smaller, more frequent meals. For example, a small breakfast, then small meals every 3 to 4 hours.
- Go easy on fatty or very high-fiber foods in the first few days of treatment.
- Skip the big meals. The advisory notes vomiting is more likely with large meals.
- Drink enough fluids, in small sips if needed.
What helps GLP-1 constipation?
The same advisory suggests:
- Enough fluids through the day.
- Fiber from foods, added slowly: fruit, vegetables, beans, whole grains.
- Ask your care team if that isn't enough. The advisory notes extra steps are often needed.
Moving more can help too. See our post on water and daily steps on a GLP-1.
When to call your care team
Get medical advice quickly if you have:
- Vomiting or diarrhea that won't stop, or you can't keep fluids down.
- Signs of dehydration, like feeling dizzy, very dark urine or peeing much less.
- Severe or ongoing belly pain, sometimes spreading to your back, with or without vomiting.
The FDA label for semaglutide says kidney injury has been reported, mostly in people who became dehydrated from stomach side effects. It also warns that severe or ongoing belly pain can be a sign of pancreatitis, which needs medical care. In an emergency, call your local emergency number.
Why log your side effects?
Side effects are easy to forget by your next appointment. A simple log helps you:
- See when they happen compared with your shot day.
- See if they ease as the weeks go by.
- Show your care team real notes when you talk about your dose.
How Ollie helps
Ollie is a GLP-1 and peptide tracker. Log your shot, then tap how you feel. Your side effects sit next to your shot days, water and steps, so patterns are easier to spot.
No account and no login. Your logs stay on your iPhone (privacy).
Related: GLP-1 water intake and daily steps · Protecting muscle on a GLP-1
GLP-1 side effects: quick answers
What are the most common GLP-1 side effects?
Nausea, diarrhea, vomiting and constipation. In a large trial, 74% of people on the medicine reported stomach or gut side effects, vs 48% on placebo.
How long do GLP-1 side effects last?
In trials they were typically short-lived and eased with time, and were most often reported while the dose was being raised. Talk to your care team if they don't ease.
What helps nausea on a GLP-1?
Expert advice suggests smaller, more frequent meals, going easy on fatty foods at first, avoiding large meals and drinking enough fluids.
What helps constipation on a GLP-1?
Enough fluids and fiber from foods, added slowly. Ask your care team if you need more help.
Sources
- Wilding JPH et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med. 2021;384(11):989–1002. Link
- US FDA. Semaglutide prescribing information, sections 5.2 (pancreatitis), 5.5 (acute kidney injury) and 6.1. PDF
- Gorgojo-Martínez JJ et al. Clinical recommendations to manage gastrointestinal adverse events in patients treated with GLP-1 receptor agonists: a multidisciplinary expert consensus. J Clin Med. 2022;12(1):145. Link
- Mozaffarian D et al. Nutritional priorities to support GLP-1 therapy for obesity: a joint advisory from ACLM, ASN, OMA and TOS. Am J Clin Nutr. 2025;122:344–367 (GI advice, p. 352). GLP-1%20Therapy%20for%20Obesity.pdf">PDF