GLP-1 medicines such as Mounjaro, Wegovy and Foundayo slow the movement of food through your digestive system, which is part of how they reduce appetite, and one consequence is that stools can become harder and less frequent. Constipation is among the most commonly reported side effects of all three, most often when you start treatment or increase a dose. The foundations of relief are drinking enough fluid, gradually increasing fibre, staying active and keeping a regular toilet routine. If those aren't enough, a pharmacist can advise on laxatives, with osmotic laxatives such as macrogol often suggested first and stimulant laxatives kept for short-term use. Seek urgent medical advice for severe abdominal pain, persistent vomiting, being unable to pass wind or stools, or rectal bleeding.
GLP-1 medicines mimic a gut hormone that slows the rate at which food leaves your stomach and travels through your intestines. That slower transit keeps you fuller for longer, which is helpful for appetite, but it also gives your colon more time to absorb water from stool, leaving it harder, drier and more difficult to pass. Several other factors often add to the effect at the same time.
| Contributing factor | Why it matters |
|---|---|
| Slower gut transit | Food and stool move through more slowly, so more water is absorbed |
| Eating less overall | Less food means less bulk in the bowel, so bowel movements become less frequent |
| Lower fibre intake | Reduced appetite often means fewer fruit, vegetables and wholegrains |
| Drinking less | Reduced thirst or nausea can lead to mild dehydration, which hardens stools |
| Less activity | Fatigue or feeling unwell can reduce movement, which normally helps the bowel |
| Other medicines | Some blood pressure, iron and pain medicines can cause constipation |
Worth knowing
Constipation is not a sign that something is going wrong, and it doesn't mean the medicine isn't suitable for you. It is a predictable effect of how these medicines work, and for most people it eases as the body adjusts. Our guides to Mounjaro tolerance and Wegovy tolerance explain how your body adapts to each dose.
Constipation appears across the whole class, so the practical advice is the same whichever treatment you use. What differs is mainly when it tends to show up and how the medicines are dosed.
| Treatment | Constipation | When it tends to appear |
|---|---|---|
| Mounjaro (tirzepatide) | Among the commonly reported side effects | When starting and after each dose increase; see our Mounjaro side effects guide and dose schedule |
| Wegovy injection (semaglutide) | Among the commonly reported side effects | When starting and after each dose increase; see our Wegovy side effects guide and dose schedule |
| Wegovy pill (semaglutide) | Among the commonly reported side effects | Particularly during dose increases; see our Wegovy pill side effects guide and dose schedule |
| Foundayo (orforglipron) | Listed as a very common side effect in the UK product information (more than 1 in 10 people) | Particularly around dose increases; see our Foundayo side effects guide and dosage guide |
- Start hereEveryday habitsFluids, gradual fibre, movement and a regular toilet routine
- If that's not enoughAsk your pharmacistAn osmotic or bulk-forming laxative may be suggested first
- If it persistsTalk to your prescriberThey can slow your dose increases or review your plan
- Any timeRed flagsSevere pain, persistent vomiting or being unable to pass wind or stools: seek urgent help
Drink Enough Fluid
Fluid keeps stools soft, and it becomes even more important if you increase your fibre. General guidance is around 1.5 to 2 litres a day, mostly water, though you may need more in warm weather or if you are exercising. If nausea makes drinking hard, take small, frequent sips rather than large amounts at once. Alcohol can add to dehydration, so see our guides on Mounjaro and alcohol, Wegovy and alcohol, Wegovy pill and alcohol and Foundayo and alcohol.
Build Up Fibre Gradually
Adults are generally advised to aim for around 30g of fibre a day. Fruit, vegetables, pulses, oats and wholegrains all contribute, and soluble fibre such as oats, ripe fruit and psyllium is often better tolerated than very coarse bran. Add fibre gradually over a week or two, and always alongside plenty of fluid, because a sudden jump in fibre without enough water can make bloating and constipation worse. Our nutrition guide has practical food ideas that work when your appetite is low.
Keep Moving
Regular activity stimulates the bowel. Even a brisk daily walk can make a noticeable difference, and it also supports the muscle-protecting habits covered in our muscle preservation guides for Mounjaro, Wegovy, the Wegovy pill and Foundayo.
Keep a Regular Routine
Try to go at a consistent time each day, often after a meal or a warm drink in the morning when the bowel is naturally most active. Don't ignore the urge when it comes, and give yourself unhurried time on the toilet. A footstool to raise your knees can help some people.
Watch Your Protein and Fibre Balance
Protein matters for protecting muscle, but a diet built mainly on protein shakes, meat and cheese can be low in fibre. Try to pair protein sources with vegetables, pulses or wholegrains at the same meal. Our calorie deficit calculator can help you plan meals that keep your intake sensible without cutting out fibre.
Over-the-Counter OptionsIf lifestyle measures aren't enough, a pharmacist can recommend a suitable laxative. It is best to speak to a pharmacist or your prescriber before starting one, particularly if you have other health conditions or take other medicines.
| Type | Examples | How it works | Points to know |
|---|---|---|---|
| Bulk-forming | Ispaghula husk, methylcellulose | Adds bulk and holds water in the stool | Needs plenty of fluid; suitable for longer-term use |
| Osmotic | Macrogol, lactulose | Draws water into the bowel to soften stool | Often suggested first for ongoing constipation; macrogol is well tolerated |
| Stimulant | Senna, bisacodyl | Stimulates the bowel muscles to contract | Best kept for short-term or occasional use, not daily |
| Stool softeners | Docusate | Softens stool | Limited evidence of benefit on its own |
Important
Don't take a laxative if you have severe abdominal pain, are vomiting, or think your bowel may be blocked. In those situations, seek medical advice immediately instead.
Most constipation on GLP-1 medicines is uncomfortable rather than dangerous, but there are situations where you should get advice promptly. Rare cases of intestinal blockage and severe constipation with impacted stool have been reported with GLP-1 medicines, which is why persistent or severe symptoms should never be ignored.
| Situation | What to do | Urgency |
|---|---|---|
| Severe or worsening abdominal pain, with or without vomiting | Seek urgent medical help (NHS 111, or 999 in an emergency) | Urgent |
| Persistent vomiting, or you can't keep fluids down | Seek urgent advice, as dehydration can become serious | Urgent |
| Unable to pass wind or stools, with a swollen, hard abdomen | Seek urgent medical help; this can be a sign of a blockage | Urgent |
| Blood in your stool or bleeding from the back passage | Contact your GP promptly | Soon |
| No improvement after a week or two of the steps above | Speak to your pharmacist, GP or prescriber about next steps | Review |
| Constipation is affecting your daily life or your willingness to continue | Talk to your prescriber; adjusting the pace of your dose increases may help | Review |
Report any suspected side effect to the MHRA through the Yellow Card scheme at yellowcard.mhra.gov.uk. If constipation is significant, your prescriber may suggest staying on your current dose for longer before increasing, which is a routine and sensible adjustment. Not sure whether treatment is suitable for you? Our guide to NHS eligibility and the BMI calculator are a good starting point, and our guide to who should not take the Wegovy pill explains who should take extra care.
What Not to Do, and How to Prevent ItWhat not to do
- Don't cut back on fluids to avoid needing the toilet, since dehydration makes constipation worse
- Don't suddenly add large amounts of bran or fibre supplements without increasing your water intake
- Don't rely on stimulant laxatives every day, as the bowel can become dependent on them
- Don't ignore several days without a bowel movement accompanied by pain, bloating or vomiting
Preventing it before it starts
- Start increasing fluids and fibre in the week before a dose increase, rather than waiting for symptoms to appear
- Keep a simple note of your bowel habits, so you notice changes early and can tell your prescriber how long they have lasted
- Don't skip meals entirely; small, regular, fibre-containing meals keep the bowel working
- Be mindful of magnesium and iron supplements, which can affect bowels, and ask your pharmacist before adding new supplements
- If you have a history of bowel problems or bowel surgery, mention it during your consultation
Small, steady changes usually work better than dramatic ones, and it is worth giving each new habit a few days to take effect before deciding whether it is helping. If you're also dealing with sickness, our guides to Mounjaro side effects and Wegovy tablets side effects cover what else to expect.
Struggling With Side Effects? We're Here to Help.
Our GPhC-registered pharmacy team can talk through constipation and other side effects as your body adjusts, including practical advice on your dose plan.
Start Your Free Online Consultation → Use code SWITCH10 if you're switching from another provider Happy Pharmacy is a GPhC-registered pharmacy (No. 9013192) — Superintendent Pharmacist: Palvinder Deol — Rated 4.8★ Excellent on Trustpilot- Mounjaro® (tirzepatide), Wegovy® (semaglutide) and Foundayo® (orforglipron) UK Summaries of Product Characteristics.
- Managing Constipation in Patients on GLP-1s. Medscape, February 2026.
- Clinical recommendations to manage gastrointestinal adverse events in patients treated with GLP-1 receptor agonists: a multidisciplinary expert consensus. J Clin Med, 2022.
- NHS. Constipation: causes, treatment and when to seek help.
- MHRA. Yellow Card scheme, reporting suspected side effects of medicines.