Constipation on Mounjaro: Causes, relief and when to worry

Constipation is a listed side effect of Mounjaro, an effective weight loss medication that mimics the effects of the hormones glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) to slow down gastric emptying. However, by slowing the time it takes food to pass through your stomach, Mounjaro can also increase water reabsorption in your colon and reduce bowel motility, resulting in constipation.

Although constipation on Mounjaro is common, here we explore how long it lasts, what you can do to relieve it, and the other digestive side effects you may get. So, you’ll have a better understanding of what to look out for, how to manage your symptoms at home, and when to seek medical advice.

Yes, constipation is listed as a very common side effect of Mounjaro when it is used for weight management. However, it is a common side effect in people who take Mounjaro to manage type 2 diabetes. In clinical trials, constipation was reported in:

• 16.8% of people on the 5mg dose
• 17.1% of people on the 10mg dose
• 11.7% of people on the maximum 15mg dose

Constipation was not listed as a side effect that led to anyone stopping Mounjaro treatment.

Mounjaro causes constipation because it slows gastric emptying, which is the rate at which food moves through the stomach into the small intestine during digestion. By delaying stomach emptying, Mounjaro can keep you feeling fuller for longer and help regulate blood sugar levels, but it can also affect gut motility and bowel movements.

When it takes longer for food to move through the stomach, the large intestine (colon) can absorb more water from stools (poo). This makes it harder to pass as your poo becomes harder and drier, resulting in constipation.

Other factors that can contribute to constipation while taking Mounjaro include reduced fluid and food intake. This is often caused by the appetite-suppressing effects of Mounjaro, which can make you feel full earlier and reduce your hunger, leading to reduced fibre and fluid intake. These are both important for regular and healthy bowel function. Some people also notice that constipation gets worse when they increase their dose as they titrate up the Mounjaro dosage schedule.

For most people, constipation while taking Mounjaro is mild to moderate and improves over time as their body gets used to tirzepatide, usually resolving within the first 4 to 6 weeks of treatment. However, this can vary from person to person and may get worse during periods of dose escalation.

If you get constipation while taking Mounjaro and it is causing you concern, lasts longer than 2 weeks, is getting worse, or is painful, speak to your doctor for more advice.

Constipation can also cause bowel obstruction which is a medical emergency. Seek emergency medical attention if you have been constipated and have not passed stool for more than 3 days and have:

• vomiting
• severe stomach pain
• not able to pass gas
• swollen or hard stomach

Although constipation is a very common Mounjaro side effect, there are several things you can do to help you stay comfortable, particularly during the first few weeks of starting treatment.

1. Stay hydrated

Water is an essential part of digestion and, alongside fibre, can help soften your poo and make it easier to pass through your digestive system. The NHS recommends that adults drink 6 to 8 glasses of fluid per day, but this may increase if you are in a hot climate, physically active for long periods, or recovering from illness.

The following drinks count towards your daily fluid intake:

• water
• low-fat milk drinks
• sugar-free drinks including tea and coffee

The best way to keep yourself hydrated is to take sips of fluid regularly throughout the day, rather than waiting until you are very thirsty, as this can be an early sign of dehydration.

2. Gradually increase your fibre intake

Fibre adds bulk to your stools, making them easier to pass and helping prevent or relieve constipation. Government guidelines recommend that you should consume 30g of fibre per day as part of a healthy, balanced diet. If you are not used to eating that much fibre, you should increase your intake slowly to avoid digestive discomfort, such as bloating. You can do this by adding fibre to each meal or increasing the amount you eat by a small amount each day, until you reach the recommended 30g.

Some of the foods you should include in your diet are:

• oats
• flaxseeds
• linseeds
• berries
• sweet potatoes
• prunes
• wholemeal bread, pasta, and rice

3. Regular movement

Regular exercise is a good way to stimulate the muscles in your gastrointestinal tract and keep your bowel movements regular. Aim to complete at least 150 minutes of moderate-intensity activity each week, spread out across several days. You can also help to relieve digestive discomfort by taking a short, gentle walk after eating.

Another factor that can help manage or relieve constipation is the gastrocolic reflex. This is the body’s natural reaction that causes the colon to contract after eating. Because the gastrocolic reflex is most active in the morning and just after eating a meal, using the toilet after having breakfast can help you to establish a daily routine and prevent constipation.

4. Over-the-counter constipation relief medications

It is possible to still get constipation even though you are following a healthy, high-fibre diet, getting regular exercise, and staying hydrated. So, you may need to try a stool softener or laxative to help get things moving through your digestive system. However, you should speak to your doctor before taking any prescribed, over-the-counter, or herbal supplements for constipation.

Some common over-the-counter medications include:

• psyllium husk – works as a bulk-forming laxative by absorbing water in the gut to help soften stools and make them easier to pass
• docusate – a stool softener that works by increasing the amount of water in your poo, making it easier to pass
• Movicol – an osmotic laxative that draws water into the bowel to soften hard stools
• polyethylene glycol – also an osmotic laxative that works similarly to Movicol

5. Speak to your doctor about dose timing

If you find that constipation returns or gets worse when your dose increases, speak to your doctor about remaining on a lower dose for longer to allow your body more time to adjust to the medication. They may also be able to recommend medications to help you manage constipation to make your weight loss journey more comfortable.

Although mild constipation is common and can often be managed at home, there are certain circumstances where it is important to get medical advice. If you have constipation that lasts longer than a week despite making changes to your diet, increasing your fluid intake, and trying over-the-counter laxatives under the direction of your doctor, contact your GP. You may need your dose to be adjusted, further tests, or an alternative weight loss medication.

If you get any of the following symptoms, get urgent medical attention, or in an emergency, call 999:

• severe stomach pain or bloating that gets worse or does not improve with painkillers
• bleeding from your rectum
• blood in your stools, which can be either dark and tarry or bright red
• unexplained weight loss that was not expected during Mounjaro treatment
• feeling sick or vomiting, particularly if you are unable to keep water down
• severe stomach pain that radiates to your back and you are being sick
• unable to pass a stool or wind, which could indicate a bowel obstruction
• constipation with a fever

Constipation isn’t the only digestive side effect of Mounjaro. It can also cause diarrhoea, feeling sick, being sick, and bloating. These are also usually mild and improve as your body gets used to treatment. However, each affects your digestive system differently and may require different steps to manage it.

You may experience more than one digestive side effect at the same time. For example, constipation can contribute to bloating, while diarrhoea may occur with nausea or vomiting. These effects are often more noticeable when you first start Mounjaro or increase your dose.

Speak to your doctor if a side effect is persistent, gets worse, or is difficult to manage. Vomiting and diarrhoea can cause dehydration, so seek advice if diarrhoea doesn’t improve after a week or if you cannot keep fluids down or notice signs such as dark urine, dizziness or urinating less often. Get urgent medical advice for severe or persistent abdominal pain, particularly if it spreads to your back or occurs with vomiting, as this may indicate pancreatitis.

Constipation is a very common side effect of both Mounjaro and Wegovy when they are used for weight management. Neither medication is guaranteed to cause it, and your individual response may depend on factors such as your dose, diet, fluid intake, activity levels, and existing digestive health.

Mounjaro contains tirzepatide, while Wegovy contains semaglutide. Although they work slightly differently, both active ingredients reduce appetite and slow the movement of food through the stomach. Eating and drinking less than usual may also contribute to harder or less frequent stools.

Symptoms are often more noticeable at the start of treatment and after each dose increase. You can often help manage the symptoms by making sure that you drink enough fluid, gradually increase your fibre intake, and stay active. Mounjaro can also cause other digestive problems, such as feeling or being sick, diarrhoea, and bloating. You can find out more in our Mounjaro side effects guide.

• How to get more fibre into your diet, NHS [accessed 04 August 2026]
• Mounjaro KwikPen 2.5mg solution for injection in pre-filled pen, electronic medicines compendium (emc) [accessed 04 August 2026]
• Physical activity guidelines for adults aged 19 to 64, NHS [accessed 04 August 2026]
• Physiology, Gastrocolic Reflex, National Library of Medicine [accessed 04 August 2026]
• Water, drinks and hydration, NHS [accessed 04 August 2026]
• Wegovy 0.25 mg, FlexTouch solution for injection in pre-filled pen, electronic medicines compendium (emc) [accessed 04 August 2026]