Can Mounjaro Cause Constipation, Diarrhoea & Sickness?

Constipation is a recognised and relatively common side effect of Mounjaro.

Many people notice changes in their bowel habits when starting treatment or after increasing their dose.

Although it can be uncomfortable, it is usually mild to moderate and tends to improve as the body adjusts to the medication.

Can Mounjaro cause constipation?

Yes, constipation has been consistently reported in clinical trials of Mounjaro.

In large studies such as the SURMOUNT and SURPASS trials, around 6-11% of people experienced constipation.

It was more common at higher doses and was most likely to occur during the first few weeks of treatment or after a dose increase.

Most cases were temporary and did not require stopping the medication.

Why does Mounjaro cause constipation?

Mounjaro works by activating GLP-1 and GIP receptors, which slow down how quickly food moves through the digestive system. This slowing of gut movement allows more water to be absorbed from the stool, making it harder and drier.

Reduced appetite and eating smaller meals can also lower overall fibre and fluid intake, which can worsen constipation.

These effects are part of how Mounjaro helps control appetite, but they can temporarily disrupt normal bowel function while your body adapts.

How to stop constipation on Mounjaro

• Drink plenty of fluids throughout the day; aim for pale-yellow urine (this helps to soften the contents of your stomach and avoids dehydration which can make constipation worse)
• Gradually increase fibre intake (for example vegetables, oats, seeds), avoiding sudden large increases
• Increase physical activity, such as taking a daily walk to stimulate bowel movement
• Establish a regular toileting routine, especially after meals
• Avoid straining; give yourself time and privacy in the bathroom
• Consider gentle osmotic laxatives (such as lactulose or macrogols) if needed, following medical advice

Most people find constipation improves within one to four weeks as their body adapts.

Seek medical advice if constipation lasts more than 7–10 days or is associated with severe abdominal pain, bloating, or vomiting.

Diarrhoea is one of the most common gastrointestinal side effects of Mounjaro.

Although it can be distressing, it is usually temporary and most noticeable when starting treatment or increasing the dose.

Can Mounjaro cause diarrhoea?

Yes, diarrhoea is frequently reported in people taking Mounjaro.

In clinical trials, around 12-23% of participants experienced diarrhoea, with higher rates seen at higher doses.

It typically appeared in the early weeks of treatment and often settled as the body adjusted.

Why does Mounjaro give you diarrhoea?

Mounjaro alters digestive hormone signalling and gut motility. It can change how bile acids are processed and how fluid moves through the intestines, which can loosen stools.

Slower stomach emptying combined with increased fluid entering the intestine can also contribute. Dietary changes, such as eating smaller meals or different foods, may further affect bowel movements.

These changes are part of how the medication works and usually stabilise over time.

How to stop diarrhoea on Mounjaro

• Eat small, bland meals such as bananas, rice, toast, and oats
• Avoid fatty, spicy, or very sugary foods
• Drink fluids regularly to prevent dehydration (water or oral rehydration solutions)
• Eat slowly and avoid large meals
• Limit caffeine and alcohol (further reading: Mounjaro and alcohol)
• Allow your digestive system time to adapt, especially after starting or increasing your dose
• Consider short-term anti-diarrhoeal medication if advised by a healthcare professional

Diarrhoea usually lasts a few days to a few weeks and often settles as your body adjusts.

Seek medical advice if it lasts more than 3-5 days, causes signs of dehydration, or is accompanied by fever, severe pain, or blood in the stool.

Nausea is the most commonly reported side effect of Mounjaro.

Many people feel sick when starting treatment, but for most, this improves with time.

Can Mounjaro make you sick?

Yes, nausea is the most frequent side effect seen with Mounjaro.

In clinical trials, around 15-29% of people reported feeling sick, while vomiting occurred in about 5-12%.

Nausea was more likely during dose increases and in the early stages of treatment.

Why are you feeling sick on Mounjaro?

Mounjaro slows down how quickly the stomach empties and acts on appetite centres in the brain.

This can cause a sensation of fullness, bloating, or queasiness, especially after eating larger meals or rich foods.

The digestive system also becomes more sensitive to dietary triggers such as fatty meals or alcohol. These effects are part of the medication’s mechanism of action and usually ease as your body adapts.

How to stop feeling sick on Mounjaro

• Eat smaller meals more frequently rather than large meals
• Avoid rich, fatty, or heavily spiced foods
• Eat slowly and stop before feeling overly full
• Take small, frequent sips of water to stay hydrated
• Avoid lying down immediately after eating
• Try ginger or peppermint tea to help settle nausea
• Take your injections on the same day each week
• Follow the recommended dose-escalation schedule
• Limit alcohol intake

Nausea usually improves within one to four weeks as your body adapts.

Seek medical advice if nausea is severe, persistent, associated with vomiting, or prevents you from keeping fluids down.

Further reading: Mounjaro side effects

For most people, gastrointestinal side effects such as constipation, diarrhoea, and nausea are temporary.

They are most common in the first few weeks of treatment or after a dose increase and typically improve within two to four weeks.

In clinical trials, only around 3-7% of people stopped Mounjaro due to side effects, indicating that the majority were manageable and short-lived.

You should contact a healthcare professional promptly if you experience any of the following while taking Mounjaro:

• Severe or persistent abdominal pain, especially if it is not improving or is getting worse
• Repeated or ongoing vomiting that prevents you from keeping fluids down
• Signs of dehydration, such as very dark urine, dizziness, dry mouth, or feeling faint
• Diarrhoea lasting more than 3-5 days despite self-care measures
• Constipation lasting more than 7-10 days or associated with significant bloating or pain
• Blood in your stools or black, tarry stools
• Fever or chills alongside gastrointestinal symptoms
• Yellowing of the skin or eyes (which may suggest a gallbladder problem)
• Severe upper abdominal pain that may spread to the back, with or without vomiting (possible pancreatitis)
• Rapid or unexplained weight loss beyond what would normally be expected on treatment

Constipation, diarrhoea, and nausea are common side effects of Mounjaro, particularly when starting treatment or increasing the dose.  

These symptoms occur because the medication slows digestion and alters gut hormones. For most people, they are temporary, improve within a few weeks, and can be managed with dietary adjustments, hydration, and pacing dose increases.  

The majority of patients tolerate Mounjaro well and do not need to stop treatment due to side effects. 

Mounjaro can cause constipation, diarrhoea, and nausea, especially early in treatment or after dose increases.  

These side effects are common, expected, and usually temporary. They happen because the medication slows digestion and changes gut hormone activity. Most people find that symptoms settle within a few weeks and can be managed with simple lifestyle adjustments.  

If symptoms are severe, persistent, or concerning, medical advice should be sought.