Constipation affects up to 1 in 4 Mounjaro users, making it one of the most frequently reported gastrointestinal side effects. While rarely dangerous, it can be uncomfortable and persistent. Understanding the cause helps you address it effectively.
Why Mounjaro Causes Constipation
Tirzepatide slows gastric emptying—the rate at which food moves from the stomach into the small intestine. This delayed transit extends through the entire digestive tract, meaning stool spends longer in the colon, where more water is absorbed. The result is harder, less frequent bowel movements.
Reduced food intake also plays a role. Less food means less bulk moving through the gut, which decreases the mechanical stimulation that triggers peristalsis.
Dietary Strategies
- Increase fibre gradually: Aim for 25–30 g per day from vegetables, fruits, oats and wholegrain bread. Add fibre slowly to avoid bloating.
- Drink plenty of water: At least 1.5–2 litres daily. Fibre without adequate fluid can worsen constipation.
- Include natural laxative foods: Prunes, kiwifruit, flaxseed and chia seeds have good evidence behind them.
- Limit binding foods: White rice, bananas and excessive cheese can slow things further.
Lifestyle Adjustments
- Move daily: Even a 20-minute walk stimulates gut motility.
- Establish a routine: Try to use the toilet at the same time each day, ideally after breakfast when the gastrocolic reflex is strongest.
- Positioning: A small footstool under your feet on the toilet (the “squatty potty” position) straightens the anorectal angle and eases bowel movements.
Over-the-Counter Options
If dietary changes are not enough, your pharmacist can recommend:
- Macrogol (Laxido/CosmoCol): An osmotic laxative available without prescription in UK pharmacies. It draws water into the bowel and is safe for regular use.
- Psyllium husk (Fybogel): A bulk-forming laxative that works well with adequate fluid.
- Senna or bisacodyl: Stimulant laxatives for occasional use only—not suitable for daily long-term use.
When to See Your GP
Seek medical advice if you have not had a bowel movement for more than five days, if you notice blood in your stool, or if you experience severe abdominal pain. Your GP may investigate further or adjust your Mounjaro dose.
Does Constipation Improve Over Time?
For many users, constipation is worst during the first few weeks of treatment and at each dose increase. As your body adjusts to tirzepatide, gut motility often partially recovers. However, some people experience ongoing constipation throughout treatment. If that is you, a combination of daily fibre supplementation, adequate hydration and regular physical activity forms the best long-term management strategy.
Constipation on Mounjaro is manageable with the right combination of hydration, fibre, movement and, when necessary, pharmacy-grade laxatives.