Side Effects · 12 April 2026 · 9 min read

Constipation on Mounjaro and Wegovy — Why It Happens and How to Fix It (UK 2026)

Constipation is one of the most common GLP-1 complaints — and one of the most frustrating. Here's why it happens on Wegovy and Mounjaro, and 8 things that actually work.

Last updated: April 2026 | 9 min read

Constipation is one of the most common complaints in UK GLP-1 support groups — and one of the most frustrating. You're doing everything right, losing weight, feeling good — and then you can't go to the loo for days.

Here's everything you need to know, including what actually works.

Why Do Mounjaro and Wegovy Cause Constipation?

Both medications slow down how quickly food moves through your digestive system. This is actually part of how they work — slowing gastric emptying makes you feel fuller for longer. But the same mechanism also slows your bowels down, meaning stool moves more slowly and dries out, making it harder to pass.

On top of that, because your appetite is suppressed you're likely eating less — which means less fibre and less fluid than usual, both of which make constipation worse.

How common is it?

• Around 24% of Wegovy users experience constipation
• Around 6–7% of Mounjaro users report constipation, increasing slightly at higher doses
• It tends to be worst during the dose escalation phase and improves as your body adjusts

The good news: for most people it's temporary and very manageable.

How Long Does It Last?

Constipation on GLP-1 medications typically lasts around 47 days on average as your body adjusts. It tends to be worse when you first start or increase your dose, and improves over time.

If constipation is severe or persists beyond a few weeks without improvement, speak to your prescriber.

8 Things That Actually Help

1. Drink More Water — A Lot More

This is the single most important thing. Aim for 2–3 litres of water every day. When you're eating less, it's easy to drink less too — but your bowels need fluid to keep things moving.

If plain water is boring, try herbal teas, add lemon or cucumber, or use electrolyte tablets to make it more appealing.

HIGH5 Zero Electrolyte Tablets on Amazon →

2. Add Fibre to Every Meal

The NHS recommends 30g of fibre daily. Most people on GLP-1s eat much less than this because their portions are smaller. Focus on:

Soluble fibre (softens stool) — oats, avocado, flaxseeds, beans, apples, pears
Insoluble fibre (adds bulk) — vegetables, wheat bran, nuts, seeds, dried fruit

Add a tablespoon of flaxseeds to your yogurt or porridge — easy win.

3. Take a Fibre Supplement

When diet alone isn't enough, a fibre supplement like Fybogel (psyllium husk) is brilliant. It's gentle, effective and available from any pharmacy or on Amazon.

Fybogel Orange Sachets on Amazon →

Take it with a full glass of water and increase the dose gradually to avoid bloating.

4. Try Magnesium

Magnesium is an osmotic laxative — it draws water into the bowel to soften stool. It's also brilliant for sleep and muscle cramps, which are common complaints on GLP-1s. Take it in the evening.

Magnesium glycinate is the best-absorbed form and the gentlest on the stomach. Nutrition Geeks make a popular 3-in-1 version that's well reviewed and available on Amazon.

Nutrition Geeks Magnesium Glycinate 3 in 1 on Amazon →

5. Move Your Body Daily

Even a 15–20 minute walk every day helps stimulate your intestines and get things moving. Exercise is one of the most underrated constipation remedies — your gut responds to movement.

6. Eat Prunes or Drink Prune Juice

Old fashioned but genuinely effective. Prunes contain sorbitol which naturally softens stool. A small glass of prune juice in the morning can make a noticeable difference within 24 hours.

7. Try Kefir or Probiotic Yogurt

Gut bacteria play a huge role in bowel regularity. Adding kefir, probiotic yogurt, kimchi or sauerkraut to your diet helps restore healthy gut bacteria which supports bowel function — especially important when you're eating less than usual.

8. Use an Osmotic Laxative if Needed

If home remedies aren't working after a few days, an osmotic laxative like Macrogol (Movicol) is the recommended first-line option from the NHS. It's gentle, non-habit forming and very effective — it works by drawing water into the bowel to soften stool rather than stimulating the gut. Available from pharmacies and on Amazon.

Movicol Ease Flavour Free on Amazon →

Avoid stimulant laxatives like senna for regular use — they can cause dependency over time.

What NOT to Do

• Don't ignore it — constipation that goes untreated can lead to haemorrhoids and anal fissures
• Don't use strong laxatives regularly — use osmotic laxatives (Movicol/Laxido) rather than stimulant laxatives long term
• Don't cut fibre out — some people avoid fibre thinking it causes bloating, but removing it makes constipation worse
• Don't stop your medication — constipation is manageable and usually temporary

When to See a Doctor

Speak to your GP or prescriber if:

• Constipation lasts more than 2 weeks without improvement
• You have severe abdominal pain or bloating
• You notice rectal bleeding
• You are completely unable to pass stool or gas
• You feel very unwell alongside constipation

These could indicate a more serious issue that needs medical attention.

Does Constipation Affect Weight Loss?

You might notice the scales going up slightly when constipated — this is just the weight of stool in your gut and is temporary. It's not fat gain and will resolve once your bowels are moving normally. Don't be disheartened by a temporary scale increase during constipation.

Quick Summary

• Constipation affects around 6–24% of GLP-1 users depending on the medication
• It's caused by slower digestion and reduced food and fluid intake
• Usually temporary — most people see improvement within 4–8 weeks
• Best remedies: drink 2–3 litres of water daily, add fibre, take Fybogel or magnesium citrate, walk daily
• If needed: Macrogol (Movicol/Laxido) is the recommended laxative
• See a doctor if symptoms are severe or persistent

→ Managing nausea on GLP-1s
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This article is for informational purposes only and does not constitute medical advice. Always consult a UK-registered healthcare professional if you have concerns about side effects.

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