How to Manage Constipation on GLP-1 UK

Constipation is one of the most common side effects of GLP-1 medication — reported in approximately 12–17% of Mounjaro users in clinical trials. It is caused by the medication’s mechanism of action rather than incidental factors, and it can range from mildly inconvenient to significantly uncomfortable. Understanding why it happens is the first step to managing it effectively.

Quick answer: GLP-1 constipation is caused by slowed gut motility — the medication slows gastric emptying, which also slows the entire digestive process. The most effective interventions are: increasing fluid intake, increasing dietary fibre, gentle movement (particularly walking), and — if dietary approaches are insufficient — psyllium husk or a gentle osmotic laxative (not stimulant laxatives, which can worsen the cycle).

Why GLP-1 causes constipation

GLP-1 receptors are present throughout the gastrointestinal tract. Activation of these receptors slows peristalsis — the rhythmic muscular contractions that move food and waste through the digestive system. This effect is intentional in terms of the medication’s appetite-suppressing mechanism (slower gastric emptying means food stays in the stomach longer, increasing fullness), but it extends through the intestines in ways that cause constipation.

The problem is compounded by reduced food intake (less digestive bulk), reduced fluid intake (suppressed thirst), and reduced physical activity in the early weeks of treatment.

What makes GLP-1 constipation worse

Low fluid intake — particularly common as thirst is suppressed alongside appetite
Low fibre intake — when eating less food, fibre intake often falls sharply
Sedentary behaviour — physical activity directly stimulates gut motility; less movement means slower gut
Low-fibre food choices — proteins and fats produce less digestive bulk than fibre-rich foods
Ignoring the urge to go — gut signals become weaker when constipation persists; acting promptly matters

What actually helps

Intervention	How it helps	Practical approach
Increased water intake	Softens stool; supports gut motility	Aim for 2–2.5 litres per day; drink before meals
Dietary fibre increase	Adds bulk; stimulates peristalsis	Add vegetables, legumes, oats to every meal; aim for 25–30g fibre per day
Psyllium husk	Soluble fibre that absorbs water and forms gel; gentle bulk laxative	1 tsp in large glass of water before bed; always take with full glass of water
Walking	Physical activity directly stimulates gut motility	Even a 15-min post-meal walk accelerates transit
Warm drinks	Warm water stimulates gut contractions	Warm water with lemon in the morning; herbal tea throughout the day
Osmotic laxatives (macrogol — e.g. Movicol)	Draws water into bowel to soften stool; safe for regular use	Available over the counter; discuss with pharmacist if needed

What to avoid

Stimulant laxatives (senna, bisacodyl) for regular use: these force gut contractions and can cause dependency; appropriate for occasional severe constipation but not as a routine fix
Reducing fibre suddenly: abrupt fibre reduction worsens constipation rapidly; build fibre gradually if increasing from a low baseline
Ignoring constipation for more than 5–7 days: persistent constipation on GLP-1 warrants a conversation with your prescriber — dose adjustment or additional medication may be appropriate

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