Can You Get Diarrhoea From Mounjaro? (October 2026)

01 · The short answer

Yes, Mounjaro can cause diarrhoea, and it is common

Mounjaro (tirzepatide) can cause diarrhoea, and it is listed among the most common side effects. Nausea, diarrhoea, vomiting, constipation and abdominal discomfort each affect more than 1 in 10 people.¹¹³ Most side effects from this medicine are digestive, and they follow a pattern: they appear in the first days after starting or increasing a dose, peak early and settle as your body adapts.¹

Tirzepatide activates two gut-hormone receptors, GIP and GLP-1, which among other things slow how quickly the stomach empties.¹

Not everyone gets it. Many people have no bowel changes, and others have one rough week after a dose increase. Having diarrhoea does not mean the medicine is unsafe for you, but it is worth telling your prescriber so they can adjust the plan if needed.

02 · What to do

What to do if you have diarrhoea on Mounjaro

Start with fluids and food choices, then contact your clinical team if symptoms are heavy or do not settle. Practical steps for digestive effects are to eat smaller meals slowly, stop at the first feeling of fullness, favour plain lower-fat foods while adjusting, stay well hydrated and avoid lying down straight after eating.¹ Our step-by-step page on how to stop diarrhoea from Mounjaro goes through these in more detail.

If a new dose is hard to tolerate, prescribers can hold the current dose longer before stepping up. Speak to your clinical team rather than pushing through severe symptoms.¹ If you cannot keep fluids down, contact your clinical team — dehydration needs medical help straight away.¹

A pharmacist can talk through your symptoms and your other medicines in person, which is a sensible first step for mild, ongoing looseness. Report any suspected side effect through the Yellow Card scheme.¹⁹

03 · Getting Mounjaro

If you are thinking about starting Mounjaro

Treatment is supplied only after a free online consultation reviewed by a GPhC-registered prescriber, and our team offers ongoing monthly reviews and side-effect support. You can start your free consultation.

• Step 1: complete a short, free online consultation, with no obligation.
• Step 2: a GPhC-registered prescriber reviews it. Payment is taken when you place the order; if the prescriber decides the treatment is not suitable, the order is refunded automatically in full.
• Step 3: we dispense and dispatch, with same-day dispatch when ordered by 3pm, and free next-day tracked delivery in discreet, temperature-controlled packaging.

04 · Trial rates by dose

How common is diarrhoea at each dose?

In the trials behind Mounjaro's weight-management licence, diarrhoea was reported by 18.7% of people on 5mg, 20.8% on 10mg and 22.5% on 15mg, compared with 7.8% on placebo.¹ Rates rise a little with dose, but they are in the same range across strengths.

Nausea, vomiting and diarrhoea were more common while the dose was being increased and became less frequent over time.¹ Only a small share of people stopped treatment for stomach reasons. In SURMOUNT-1, 4.3% of people on 5mg, 7.1% on 10mg and 6.2% on 15mg stopped treatment because of side effects of any kind, compared with 2.6% on placebo.²

These are trial figures, and your own experience may differ.

05 · When it starts and how long

How long does Mounjaro diarrhoea last?

For most people, diarrhoea eases within days to a few weeks as the body adjusts.¹ It tends to appear in the first days after starting or increasing a dose and to peak early, then settle.¹ That is one reason Mounjaro uses a gradual dose ladder.

Because each step up can bring a fresh wave, you may notice looser stools again after moving from one strength to the next, even if the previous dose felt fine. Our guides on how soon after a dose diarrhoea appears and how long it lasts cover the timeline in more depth.

If symptoms are not settling, or a dose is hard to tolerate, tell your clinical team. They can hold your current dose for longer before stepping up.¹

06 · What helps

Practical steps that help

The most useful steps are gentle: smaller meals, plain foods and plenty of fluid. The practical steps for digestive effects are:¹

• Eat smaller meals, and eat them slowly.
• Stop at the first feeling of fullness.
• Favour plain, lower-fat foods while you adjust.
• Stay well hydrated.
• Avoid lying down straight after eating.

If you wonder which foods to avoid, plain, lower-fat choices while your gut settles are easier than rich or heavy meals. Mention any pattern you notice with meals to your prescriber.

If looseness continues, a pharmacist can advise on options that suit you and fit with your other medicines. Do not combine over-the-counter remedies without checking first.

07 · Dehydration and eating too little

Dehydration and eating too little

Diarrhoea matters mainly because of fluid loss. If you cannot keep fluids down, contact your clinical team — dehydration needs medical help straight away.¹

Eating very little is a separate issue. Mounjaro helps you feel fuller sooner and less hungry between meals,¹ but the treatment works alongside a reduced-calorie diet, not an extreme one. Fatigue, a recognised common side effect, partly reflects the body adjusting and simply eating less. Keeping meals balanced, protein especially, staying hydrated and keeping gentle activity going all help. Tell your clinical team if tiredness is severe or not settling.¹

Temporary hair shedding is also linked to rapid weight loss itself, and protein intake and overall nutrition matter, so a balanced diet is worth protecting even when your appetite is small.¹

08 · Constipation and bowel changes

Does Mounjaro affect bowel movements in other ways?

Yes. Mounjaro can push your bowels in either direction. Constipation is very common on Mounjaro for weight management (it may affect more than 1 in 10 people), because food moves through the gut more slowly and many people eat and drink less.¹ Some people alternate between the two, which is not unusual while the dose is changing.

For constipation, prioritise fluids, add fibre from vegetables and whole grains, and keep up daily movement. If it persists, a pharmacist can recommend a suitable laxative, and you should contact your clinical team for pain, bloating or more than a few days without a bowel movement.¹

Other common effects include indigestion, reduced appetite, dizziness, reflux and burping.¹ If something about your bowel changes worries you, ask your pharmacist or prescriber.

09 · When to seek help

When diarrhoea needs medical attention

Seek immediate medical help for severe, persistent stomach pain that may spread to your back, with or without vomiting, as this can signal pancreatitis.¹ Also seek immediate medical help for pain in the upper right abdomen, fever or yellowing of the skin or eyes, which can signal gallbladder problems, and for signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing.¹

Get medical help straight away if you cannot keep fluids down, and tell your clinical team if symptoms are severe or not settling. If you take insulin or a sulfonylurea alongside Mounjaro, watch for low blood sugar (shakiness, sweating, confusion), as your prescriber may need to adjust those medicines.¹

You can report any suspected side effect to the MHRA via the Yellow Card scheme.¹⁹ If you are unsure whether your symptoms are typical, our page on whether diarrhoea on Mounjaro is normal may help.

10 · Stopping and what to expect

If you stop Mounjaro, will the diarrhoea go?

Tirzepatide has a half-life of about five days, so after a final dose it takes roughly 4–5 weeks to clear the system. There is no way to speed this up, and nothing needs doing while it clears.¹ If side effects are troubling you, speak to your prescriber before stopping, since adjusting the plan, such as holding a dose for longer, is often possible.

Our pages on whether you can get withdrawals from Mounjaro and whether you can withdraw from Mounjaro cover that question separately.

Mounjaro is licensed for adults with a BMI of 30 or above, or 27 to 30 with a weight-related condition, and is used alongside a reduced-calorie diet and increased physical activity. A prescriber will assess your medical history and current medicines before deciding whether it is suitable. Individual results vary, and this page is information, not a substitute for medical advice.¹