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Side effects

Constipation on a GLP-1 medicine

Nausea gets the attention, but constipation is often the side effect that lingers. It builds quietly — less food, less fibre, less water, and a gut that is moving more slowly on purpose. The good news is that it usually responds to the basics. The important news is that, rarely, it is a sign of something that cannot wait.

By the Cafeity teamUpdated 6 min read

The short answer

Constipation is one of the most common GLP-1 side effects: in the weight-management trials it was reported by 24% of people on semaglutide 2.4 mg (11% on placebo), up to 17% on tirzepatide (5%), 19.4% on liraglutide 3 mg (8.5%) and up to 27% on orforglipron (9%).1234 A 2025 joint nutrition advisory recommends adequate fluids and fibre from food first, with fibre supplements or laxatives as options to discuss with a clinician.5 Severe stomach pain, a swollen abdomen, vomiting, or being unable to pass stool or wind needs urgent medical attention.

Bar chart of constipation in the weight-management trials: semaglutide 2.4 mg 24% versus 11% on placebo; tirzepatide up to 17% versus 5%; liraglutide 3 mg 19.4% versus 8.5%; orforglipron up to 27% versus 9%.
Share of trial participants who reported constipation, from each medicine's US prescribing information. Not a head-to-head comparison — each medicine was tested in its own trials.

How common it is

Constipation appears on every GLP-1 label as a common reaction, and at weight-management doses it is reported by roughly one person in five.

Constipation in placebo-controlled trials, from the current US prescribing information.
Medicine (trial population)PlaceboMedicine
Semaglutide 2.4 mg weekly injection (weight management)11%24%
Semaglutide 7.2 mg weekly injection (weight management)8%20% (19% on 2.4 mg in the same trials)
Tirzepatide weekly injection (weight management)5%17% (5 mg), 14% (10 mg), 11% (15 mg)
Liraglutide 3 mg daily injection (weight management)8.5%19.4%
Orforglipron daily tablet (weight management)9%20% (5.5 mg), 27% (9 mg), 24% (17.2 mg)
Semaglutide weekly injection (type 2 diabetes)1.5%5% (0.5 mg), 3.1% (1 mg)
Tirzepatide weekly injection (type 2 diabetes)1%6% (5 mg), 6% (10 mg), 7% (15 mg)

Unlike nausea, constipation does not simply rise with the dose — on tirzepatide it was reported slightly less at the higher doses.2 It is also the reaction most likely to persist after the queasy early weeks, which is why it is worth getting ahead of rather than waiting out.

Why it happens

Three things stack up. The medicines slow the movement of food through the stomach — tirzepatide's label notes the effect is strongest after the first dose.12 People eat noticeably less, which means less bulk and often less fibre reaching the bowel. And a smaller appetite usually comes with a smaller thirst, so fluid intake drops too.

Each on its own might be manageable. Together, they are a recipe for harder, less frequent stools — and the fix is mostly about putting back the fibre and fluid that the appetite change quietly took away.

What the guidance suggests

The 2025 joint advisory on nutrition during GLP-1 therapy — from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association and The Obesity Society — puts it in this order:5

  1. Adequate fluids. Drinking enough is the first step; a smaller appetite makes it easy to fall behind without noticing.
  2. Fibre from food. Vegetables, fruit, pulses, wholegrains, nuts and seeds. US reference intakes are about 25 g a day for women and 38 g for men up to 50; UK guidance is 30 g for adults.67
  3. If that is not enough, the advisory lists options clinicians use — fibre supplements, magnesium citrate, polyethylene glycol, or a stool softener to avoid straining. Which one, and how much, is a question for a pharmacist or prescriber, especially if you take other medicines.

Two practical notes. Fibre works best increased gradually and with fluid alongside it — adding a lot at once can cause bloating, which on a slower gut is no small thing. And physical activity helps keep the bowel moving in general — even a daily walk counts.

The fibre and water calculators show the reference figures Cafeity uses: fibre intake and water intake.

Fibre that fits a smaller appetite

When portions shrink, fibre has to come from denser sources. Some that work well in small amounts:

  • Pulses — lentils, chickpeas and beans carry fibre and protein together, which matters when every mouthful has to earn its place. Boiled lentils have about 8 g of fibre per 100 g; black beans about 9 g.8
  • Oats and wholegrains — porridge, wholegrain bread, brown rice.
  • Fruit with skin, and berries.
  • Vegetables — cooked often sit more comfortably than large raw salads on a slow stomach.
  • Nuts and seeds — almonds have about 12 g of fibre per 100 g, though they are energy-dense.8

If nausea is also a problem, the same advisory suggests leaning towards lower-fibre, softer foods while the nausea is at its worst, then building fibre back up.5 The two side effects pull in slightly different directions, which is one more reason to log both.

When constipation is more than constipation

Rarely, a slowed gut becomes a blocked one. The semaglutide label lists ileus, intestinal obstruction and severe constipation including faecal impaction among reactions reported after approval.1 These are uncommon, but they are emergencies, and the signs are different from ordinary constipation: severe or worsening stomach pain, a swollen or hard abdomen, vomiting, and being unable to pass stool or wind.

Severe, persistent stomach pain can also be a sign of pancreatitis or gallbladder disease, both listed in the warnings on every GLP-1 label.12

When to contact your prescriber

Keeping a record of it

Cafeity has a bowel log alongside its symptom log, so constipation can be recorded as it happens rather than reconstructed from memory — next to your fibre, water and doses on the same day. Over a few weeks the record shows whether it tracks with low-fibre days, dose increases or neither.

Cafeity Today screen: day 1 of 7 since the last dose with the estimated level at 97% of peak, fibre 21 of 25 g, protein 110 of 100 g, steps, water 850 ml of 2.4 L, the next logged dose and the weight trend.
Fibre, protein and water on the Today screen.
Cafeity weekly summary: protein 110 g a day, energy 981 kcal a day, water 925 ml a day, weight trend 86.7 kg, one symptom day and two of two days logged.
The week at a glance, including symptom days.

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Common questions

How long does GLP-1 constipation last?
The labels do not give a duration. Unlike nausea, constipation can persist beyond the early weeks, so it is usually better managed — fluids, fibre, activity, and help from a pharmacist if needed — than waited out.5
Should I take a laxative?
Ask a pharmacist or your prescriber. The joint advisory lists fibre supplements, magnesium citrate, polyethylene glycol and stool softeners as options clinicians use when food and fluids are not enough, but the right choice depends on you and your other medicines.5
Can constipation on a GLP-1 be dangerous?
Usually not, but rarely yes. Intestinal obstruction and severe constipation with faecal impaction have been reported after approval.1 Severe pain, a swollen abdomen, vomiting or being unable to pass wind are reasons to seek help urgently.
Why do I have constipation and diarrhoea?
Both appear on the labels, and some people alternate between them, particularly around dose changes. Logging each episode with the date makes the pattern much easier to discuss with your prescriber.

Sources

  1. Semaglutide injection and tablets for weight management — US prescribing information DailyMed, US National Library of Medicine, version published 30 June 2026
  2. Tirzepatide injection for weight management and obstructive sleep apnoea — US prescribing information DailyMed, US National Library of Medicine, version published 2 September 2026
  3. Liraglutide 3 mg injection for weight management — US prescribing information DailyMed, US National Library of Medicine, version published 15 June 2026
  4. Orforglipron tablets for weight management — US prescribing information DailyMed, US National Library of Medicine, version published 13 August 2026
  5. 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 Mozaffarian D et al. 2025 (published in four journals)
  6. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids Institute of Medicine, National Academies Press (2005)
  7. Carbohydrates and Health Scientific Advisory Committee on Nutrition, UK (2015)
  8. FoodData Central US Department of Agriculture, Agricultural Research Service

Written by the Cafeity team from the sources listed here. Figures from prescribing information are quoted as the label states them; trial results are averages from those trials, not predictions for any one person. This page has not yet been reviewed by a clinician — see the editorial policy for how pages are researched and corrected.