Constipation is one of the most common GLP-1 side effects, and it tends to last longer than the others. Fiber and fluids within a smaller intake are the first line of defense, and there's medical help if that isn't enough.
Why constipation is so common on GLP-1s
The exact cause isn't pinned down. The researchers behind the pooled STEP trial analysis suggest the drugs' effects on gut motility are the likely reason constipation lasts longer than other GI symptoms, though direct evidence on lower-gut transit is lacking (Wharton et al., Diabetes, Obesity and Metabolism, 2021, DOI (external link)). Eating and drinking less adds to it.
In those pooled STEP 1–3 data, covering 2,117 people on semaglutide 2.4 mg and 1,262 on placebo, constipation was reported by 24.2% of people on semaglutide and 11.1% on placebo, making it the fourth most frequent GI effect after nausea, diarrhea, and vomiting. Almost all GI effects were non-serious (99.5%) and mild-to-moderate (98.1%), and they were most frequent during or shortly after dose increases. A meta-analysis of 19 randomized trials covering 32,884 patients put it in relative terms: constipation was about 2.4 times as likely on a GLP-1 as on placebo (RR 2.35, 95% CI 1.94–2.85) (Tanashat et al., American Journal of Cardiovascular Drugs, 2025, DOI (external link)).
Constipation differs from the other GI effects in how long it lasts. In the STEP trials the median episode lasted 47 days on semaglutide (35 days on placebo), compared with 8 days for nausea, and the share of people with constipation leveled off around week 10 of treatment. So it's common, roughly one in four people, and a long stretch isn't unusual or a sign that treatment isn't working. In people who stayed on semaglutide after the dose-increase phase, the share with constipation did fall over time.
Diet often makes it worse. A small cross-sectional study of 69 people on a GLP-1 found average fiber intake of about 14.5 g/day, well below recommended levels (Johnson et al., Frontiers in Nutrition, 2025, DOI (external link)). Our guide on protein, fat, and carbohydrates covers this fiber gap in more detail, and our fiber guide covers how to close it.
What helps
- Fit fiber-rich foods into your smaller intake: vegetables, fruit, legumes, and whole grains, even in small portions, instead of relying only on low-fiber, easy-to-tolerate foods.
- Drink consistently. Drinking less alongside eating less is a common, often overlooked contributor.
- Move gently. Even short walks can help get things moving, alongside the strength training covered in our exercise guide.
- Ask about a fiber supplement or stool softener if diet changes aren't enough. It's a common, reasonable step, not a sign of a bigger problem.
- Keep a regular routine around meals and bathroom timing, which can help when your eating pattern has changed a lot.
When to raise it with your prescriber
Talk to your prescriber if constipation lasts more than a week despite these steps, or comes with significant abdominal pain, bloating, or nausea. Our guide on talking to your doctor about side effects that aren't improving can help. Severe, persistent constipation can occasionally point to a more significant motility problem such as gastroparesis. For the full list of symptoms that need a same-day call, see managing GLP-1 side effects.
Study findings above are attributed to their authors and were located via PubMed.
This article is for general education and is not medical advice. Talk with your prescriber or care team about your own situation.