Constipation on Mounjaro or Wegovy: fibre and fluids basics
The NHS lists constipation as a common side effect of tirzepatide (Mounjaro) and semaglutide (Wegovy). Fibre and fluids are part of normal NHS advice on constipation. This page is the food side: what that looks like in grams. It isn't treatment.
The BNF lists constipation as a common side effect of both tirzepatide (Mounjaro) and semaglutide (Wegovy). It says patients should be told about stomach and bowel side effects when the medicine is first prescribed and at each dose increase. They're usually not serious, but they can last several days and can lead to dehydration, so keep drinking fluids and speak to your prescriber, GP or pharmacist if they don't settle.
If something feels wrong, ask a professional. The NHS lists constipation, feeling or being sick, and stomach pain among the common side effects of tirzepatide (Mounjaro), and constipation among those of semaglutide (Wegovy). It says to speak to a pharmacist or doctor if you have “any side effects that bother you or do not go away”. It lists an inflamed pancreas, which “can cause severe pain in your stomach or back, which does not go away”, as a possible serious side effect of both, and says to call NHS 111 if you think you might be having serious side effects.
What the NHS says to try
To make poo softer and easier to pass, the NHS says to:
- “drink plenty of water and other fluids and avoid alcohol”
- “gradually increase the fibre in your diet”
- “add some wheat bran, oats or linseed to your diet”
- include fruits that contain sorbitol, “such as apples, apricots, grapes (and raisins), raspberries and strawberries”
It also suggests a regular toilet routine and that “a daily walk or run can help you poo more regularly”.
Those foods, in grams
- Wheat bran: 6.2g in 15g
- Porridge oats: 3.6g in 40g dry oats
- Flaxseed (linseed): 3.0g in 15g (1 tbsp)
- Raspberries: 3.0g in 80g
- Apple: 1.0g in 80g with skin
Go slowly. Adding 6g of wheat bran to a 20g day is a big jump; the NHS says gradually.
When to speak to someone
The NHS says to see a GP if you:
- “are constipated and it’s not getting better with treatment”
- “are regularly constipated”
- “have blood in your poo”
- “have tummy pain”
- notice sudden changes in how you poo (your bowel habits)
It also says to “speak to a pharmacist if diet and lifestyle changes are not helping”, and to “speak to the GP before you stop taking any prescribed medicine”.
Not medical advice. Gutmaxx is a free food tracker, not a health service, and is not affiliated with the NHS. We don’t give advice on doses or on whether a medicine is right for you. Speak to your prescriber, GP or pharmacist about your medicine, your diet and any side effects. This page is general information, not medical advice. Mounjaro is a trademark of Eli Lilly and Wegovy of Novo Nordisk; neither company is connected with or endorses Gutmaxx.
More for small appetites
Last reviewed . General information, not medical advice. Speak to your prescriber, GP or pharmacist.
Sources
- NHS – Tirzepatide (Mounjaro)
- NHS – Semaglutide (Wegovy, Ozempic, Rybelsus)
- NHS – Constipation
- NHS – How to get more fibre into your diet
- NICE – Tirzepatide for managing overweight and obesity (TA1026): diet, physical activity and behavioural approaches
- Mounjaro KwikPen Summary of Product Characteristics, electronic medicines compendium (emc)
- BNF – Tirzepatide
- BNF – Semaglutide
Food figures come from each linked Gutmaxx food page, which shows its own source and check date. NHS, NICE, emc and BNF pages accessed 22 Oct 2026.