Does Mounjaro cause diverticulitis? Currently, there is no established evidence linking Mounjaro (tirzepatide) to the development of diverticulitis. This dual GIP and GLP-1 receptor agonist, licensed in the UK for type 2 diabetes and weight management, commonly causes gastrointestinal side effects such as nausea, diarrhoea, and constipation due to its effects on gut motility. However, clinical trials and post-marketing surveillance have not identified diverticulitis as a specific adverse event. Patients with pre-existing diverticular disease should discuss their gastrointestinal history with their prescriber, maintain adequate hydration and fibre intake, and monitor bowel habits whilst taking this medication.

Understanding Mounjaro and Its Gastrointestinal Effects

Mounjaro (tirzepatide) is a dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist licensed in the UK for the treatment of type 2 diabetes mellitus and, more recently, for weight management in adults with obesity (BMI ≥30 kg/m²) or overweight (BMI ≥27 kg/m²) with weight-related comorbidities. As a once-weekly subcutaneous injection, Mounjaro works by mimicking naturally occurring incretin hormones that regulate blood glucose levels and appetite.

The mechanism of action involves stimulating insulin secretion in a glucose-dependent manner, suppressing glucagon release, slowing gastric emptying, and reducing appetite through central nervous system pathways. These effects collectively improve glycaemic control and promote weight loss. However, the slowing of gastric emptying and effects on gastrointestinal motility mean that digestive side effects are among the most commonly reported adverse reactions with this class of medication.

Gastrointestinal effects are particularly relevant because they affect a significant proportion of patients initiating treatment. Understanding how Mounjaro interacts with the digestive system is essential for both healthcare professionals and patients, especially when considering potential links to specific gastrointestinal conditions. The Medicines and Healthcare products Regulatory Agency (MHRA) and the European Medicines Agency (EMA) continue to monitor post-marketing safety data for all GLP-1 receptor agonists, including tirzepatide.

It's important to note that tirzepatide has not been studied in patients with severe gastrointestinal disease, including severe gastroparesis, and is therefore not recommended in these patients. Additionally, the delayed gastric emptying effect can reduce the absorption of oral medications, including combined oral contraceptives. Women using oral contraceptives should consider additional or alternative contraception for 4 weeks after initiating tirzepatide and following dose increases.

Whilst Mounjaro has demonstrated considerable efficacy in clinical trials, patients often have questions about whether the medication might increase their risk of developing specific gastrointestinal conditions, including diverticulitis—an inflammatory condition affecting pouches (diverticula) in the colon wall.

Current Evidence on Mounjaro and Diverticulitis Risk

At present, there is no established causal link between Mounjaro (tirzepatide) and the development of diverticulitis based on available clinical trial data and post-marketing surveillance. Diverticulitis occurs when diverticula—small pouches that can form in weakened areas of the colon wall—become inflamed or infected. Risk factors for diverticulitis include advancing age, low-fibre diet, obesity, lack of physical activity, smoking, and certain medications such as non-steroidal anti-inflammatory drugs (NSAIDs) and corticosteroids.

The pivotal clinical trials for tirzepatide (SURPASS programme) did not identify diverticulitis as a specific adverse event of concern, as documented in the European Medicines Agency's European Public Assessment Report (EPAR). Gastrointestinal adverse effects were predominantly related to nausea, vomiting, diarrhoea, and constipation—symptoms consistent with the known pharmacological effects of GLP-1 receptor agonists on gastric motility. No signal suggesting an increased incidence of diverticulitis has emerged from these large-scale studies involving thousands of participants.

However, it is theoretically possible that changes in bowel habits—particularly constipation, which can occur with GLP-1 receptor agonists—might influence existing diverticular disease. Constipation can increase intracolonic pressure, which some clinicians believe may contribute to diverticular complications in susceptible individuals. Nevertheless, this remains speculative, high-quality evidence is currently lacking, and there is no official evidence linking Mounjaro specifically to diverticulitis onset.

Patients with pre-existing diverticular disease should discuss their gastrointestinal history with their prescribing clinician before starting Mounjaro. Maintaining adequate hydration, dietary fibre intake, and monitoring bowel habits are prudent measures for anyone with known diverticula, regardless of medication use. Healthcare professionals should remain vigilant for any emerging safety signals as real-world use of tirzepatide expands, and refer to NICE guideline NG147 on diverticular disease for appropriate management strategies.

Gastrointestinal Side Effects of Mounjaro

The most frequently reported adverse effects of Mounjaro involve the gastrointestinal system, reflecting the medication's mechanism of action on gut motility and appetite regulation. According to the Summary of Product Characteristics (SmPC), the most common side effects include:

• Nausea (affecting 12-24% of patients, with frequency increasing at higher doses)

• Diarrhoea (reported in 13-22% of participants)

• Vomiting (occurring in 6-10% of patients)

• Constipation (affecting 5-12% of users)

• Abdominal pain or discomfort

• Dyspepsia (indigestion)

• Decreased appetite

These effects are typically mild to moderate in severity and tend to diminish over time as the body adjusts to treatment. The gradual dose titration schedule recommended for Mounjaro—starting at 2.5 mg weekly and increasing every four weeks—is specifically designed to minimise gastrointestinal intolerance.

The slowing of gastric emptying can lead to feelings of fullness, bloating, and altered bowel patterns. Some patients experience diarrhoea, whilst others develop constipation, highlighting individual variation in response. Constipation warrants particular attention, as inadequate fluid intake combined with reduced gut motility may contribute to discomfort and, theoretically, could exacerbate pre-existing diverticular disease, though this has not been definitively established.

Rare but serious gastrointestinal adverse effects reported with GLP-1 receptor agonists include pancreatitis, gallbladder disease (cholecystitis, cholelithiasis), and severe delayed gastric emptying. Cases of gastroparesis have been reported post-marketing with GLP-1 receptor agonists, though a causal relationship has not been firmly established. If pancreatitis is suspected, tirzepatide should be discontinued immediately and urgent medical attention sought.

Patients should be aware of the risk of dehydration from gastrointestinal losses, which in severe cases could lead to acute kidney injury. Maintaining adequate fluid intake is essential, particularly if experiencing diarrhoea or vomiting.

Patient education about expected side effects, dietary modifications (eating smaller meals, avoiding high-fat foods), and maintaining hydration can significantly improve tolerability and treatment adherence. Suspected adverse reactions should be reported via the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk or the Yellow Card app).

When to Seek Medical Advice While Taking Mounjaro

Patients taking Mounjaro should be aware of warning signs that require prompt medical evaluation. Whilst mild gastrointestinal symptoms are common and often resolve spontaneously, certain symptoms may indicate more serious complications requiring clinical assessment.

Call 999 or go to A&E immediately if you experience:

• Severe, persistent abdominal pain, particularly if localised to the lower left abdomen (a common site for diverticulitis)

• Fever accompanied by abdominal pain or tenderness

• Blood in stools (either bright red or dark, tarry stools)

• Persistent vomiting preventing adequate fluid or medication intake

• Signs of dehydration (reduced urination, dizziness, dry mouth, confusion)

• Sudden onset of severe upper abdominal pain radiating to the back (potential pancreatitis)

• Yellowing of skin or eyes (jaundice, suggesting gallbladder or liver issues)

If pancreatitis is suspected, stop taking tirzepatide immediately and seek urgent medical attention.

Contact your GP or NHS 111 if:

• Gastrointestinal side effects persist beyond the first few weeks or worsen over time

• Diarrhoea persists for more than a few days or is accompanied by fever

• Constipation becomes severe or does not respond to dietary measures and over-the-counter remedies

• You experience unexplained weight loss beyond expected therapeutic effects

• Symptoms significantly impact your quality of life or ability to maintain nutrition

• You have concerns about any new or unusual symptoms

Patients with known diverticular disease should maintain regular contact with their healthcare team and report any changes in bowel habits or abdominal symptoms promptly. The NHS 111 service can provide guidance if you are uncertain whether symptoms require immediate attention. Never discontinue Mounjaro abruptly without consulting your prescriber, as this may affect diabetes control. However, if severe symptoms occur, seek medical advice immediately—your safety takes precedence over medication continuity.

Managing Digestive Health on GLP-1 Receptor Agonists

Optimising digestive health whilst taking Mounjaro involves a combination of lifestyle modifications, dietary strategies, and clinical monitoring. These approaches can minimise gastrointestinal side effects and support overall wellbeing during treatment.

Dietary recommendations include:

• Eating smaller, more frequent meals rather than large portions, which can overwhelm the slowed digestive system

• Increasing dietary fibre gradually through fruits, vegetables, whole grains, and legumes to support regular bowel movements and potentially benefit diverticular disease

• Maintaining adequate hydration—aim for 6-8 glasses of water daily, particularly important if experiencing diarrhoea or constipation

• Limiting high-fat, fried, and spicy foods that may exacerbate nausea and delayed gastric emptying

• Avoiding carbonated beverages if experiencing bloating or discomfort

• Eating slowly and chewing thoroughly to aid digestion

Lifestyle measures that support gastrointestinal health include regular physical activity, which promotes gut motility and can help prevent constipation. The NHS recommends at least 150 minutes of moderate-intensity activity weekly for adults with type 2 diabetes. Stress management techniques may also benefit digestive function, as stress can exacerbate gastrointestinal symptoms.

For constipation management, NICE Clinical Knowledge Summary guidance suggests a stepwise approach: first optimising fluid and fibre intake (introduced gradually to avoid worsening bloating), then considering appropriate laxatives based on stool consistency. Bulk-forming laxatives (such as ispaghula husk) may help with soft, poorly formed stools, while osmotic laxatives might be more suitable for hard stools. Stimulant laxatives may be used short-term if needed, but discuss with your GP or pharmacist before starting any laxative regimen.

Regular monitoring is essential. Patients should attend scheduled diabetes reviews where gastrointestinal symptoms, weight changes, and overall treatment response can be assessed. Healthcare professionals may adjust the Mounjaro dose or titration schedule based on individual tolerance. In some cases, temporary dose reduction or additional symptomatic treatment may be appropriate.

For individuals with pre-existing diverticular disease, maintaining these healthy digestive practices is particularly important. While there is no contraindication in the SmPC for using Mounjaro in patients with diverticulosis (asymptomatic diverticula), the medication is not recommended in patients with severe gastrointestinal disease. Open communication with your healthcare team ensures personalised management. If you have a history of recurrent diverticulitis, your clinician will weigh the benefits of Mounjaro against potential risks on an individual basis, considering alternative treatment options if necessary.

Frequently Asked Questions