Mounjaro (tirzepatide) is a dual GIP/GLP-1 receptor agonist licensed in the UK for type 2 diabetes and weight management. Whilst it offers significant benefits for glycaemic control and weight reduction, patients with Crohn's disease may have concerns about its gastrointestinal side effects. This article examines the use of Mounjaro in people with Crohn's disease, exploring potential risks, safety considerations, and the importance of individualised prescribing decisions. Understanding how tirzepatide interacts with inflammatory bowel disease is essential for safe and effective treatment.
Quick Answer: Mounjaro is not contraindicated in Crohn's disease, but its gastrointestinal side effects may complicate symptom assessment and disease monitoring, requiring individualised prescribing decisions and close collaboration between gastroenterology and prescribing teams.
Mounjaro (tirzepatide) is a prescription medicine licensed in the UK for the treatment of type 2 diabetes mellitus and, more recently, for weight management in adults with obesity or overweight with weight-related comorbidities. It is administered as a once-weekly subcutaneous injection and belongs to a novel class of medications known as dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonists.
The mechanism of action of Mounjaro involves mimicking two naturally occurring incretin hormones. GLP-1 stimulates insulin secretion in response to elevated blood glucose, suppresses glucagon release, slows gastric emptying, and reduces appetite. GIP also enhances insulin secretion and may influence fat metabolism and energy balance. By activating both pathways simultaneously, tirzepatide offers potent glycaemic control and significant weight reduction, which has been demonstrated in large-scale clinical trials.
In the UK, Mounjaro is regulated by the Medicines and Healthcare products Regulatory Agency (MHRA) and is available on prescription. The National Institute for Health and Care Excellence (NICE) has issued guidance on its use for type 2 diabetes and weight management. For weight management, NICE specifies eligibility criteria based on body mass index (BMI ≥35 kg/m² with comorbidities or ≥40 kg/m² without) and requires use within specialist weight management services. For diabetes, separate criteria apply regarding HbA1c levels and prior treatments.
Patients typically start on a low dose (2.5 mg weekly) with gradual titration to minimise gastrointestinal side effects. Common adverse effects include nausea, diarrhoea, vomiting, and constipation, which are generally mild to moderate and tend to diminish over time. Other important safety considerations include:
Tirzepatide is not recommended in patients with severe gastrointestinal disease, including severe gastroparesis
Risk of hypoglycaemia when used with insulin or sulfonylureas (dose reduction of these agents may be required)
Potential for gallbladder disease (cholelithiasis, cholecystitis)
Risk of dehydration leading to acute kidney injury
Reduced exposure to oral contraceptives (additional contraception recommended for 4 weeks after initiation and after each dose increase)
Patients should report suspected side effects via the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk).
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Start HereCrohn's disease is a chronic, relapsing inflammatory bowel disease (IBD) that can affect any part of the gastrointestinal tract, from the mouth to the anus, though it most commonly involves the terminal ileum and colon. The condition is characterised by transmural inflammation, which can lead to complications such as strictures, fistulae, and abscesses. Symptoms vary widely but typically include persistent diarrhoea (which may be bloody), abdominal pain and cramping, weight loss, fatigue, and reduced appetite. Extra-intestinal manifestations—such as arthritis, skin lesions, and eye inflammation—may also occur. Perianal disease, including fistulae and abscesses, is common and may require specific management approaches.
The exact cause of Crohn's disease remains unclear, but it is thought to result from a complex interplay of genetic susceptibility, environmental factors, and an abnormal immune response to gut microbiota. Diagnosis is based on a combination of clinical history, blood tests (including inflammatory markers such as C-reactive protein), faecal calprotectin (used in primary care for triage and in secondary care for monitoring), endoscopy with biopsy, and imaging studies such as MRI enterography.
Current treatment options aim to induce and maintain remission, manage symptoms, and prevent complications. According to NICE guidance (NG129) and the British Society of Gastroenterology guidelines, first-line therapy often includes corticosteroids (e.g., prednisolone or budesonide) for acute flares, followed by immunosuppressants such as azathioprine or methotrexate for maintenance. In children and young people, exclusive enteral nutrition is a first-line induction option. Biologic therapies—including anti-TNF agents (infliximab, adalimumab), vedolizumab, and ustekinumab—are reserved for moderate to severe disease or when conventional treatments fail. Nutritional support, smoking cessation, and surgical intervention may also be necessary in selected cases. Management is typically coordinated by gastroenterology specialists within multidisciplinary teams.
The Summary of Product Characteristics (SmPC) for Mounjaro does not list Crohn's disease as a specific contraindication. However, it does state that tirzepatide is not recommended in patients with severe gastrointestinal disease, including severe gastroparesis. Additionally, clinical trial data for tirzepatide did not specifically focus on patients with active inflammatory bowel disease, and real-world evidence in this population remains limited.
The primary concern relates to Mounjaro's gastrointestinal side effects. Because the medication slows gastric emptying and commonly causes nausea, vomiting, diarrhoea, and abdominal discomfort—especially during dose escalation—these effects may overlap with or exacerbate symptoms of Crohn's disease. For patients with active or poorly controlled Crohn's, distinguishing between drug-related side effects and disease flares can be challenging, potentially complicating disease monitoring and management.
That said, some patients with Crohn's disease may also have type 2 diabetes or obesity, conditions for which Mounjaro is indicated. In such cases, the decision to prescribe Mounjaro should be individualised, taking into account the current disease activity of Crohn's, the patient's symptom burden, and the potential benefits of improved glycaemic control or weight loss.
Close collaboration between the prescribing clinician (often a GP or endocrinologist) and the patient's gastroenterology team is essential to ensure safe and effective use. A clear monitoring plan should be established, including who to contact and when to check inflammatory markers or faecal calprotectin if symptoms worsen. Patients with well-controlled Crohn's disease in remission may be more suitable candidates than those experiencing active inflammation or frequent flares.
It's also important to note that tirzepatide can reduce the absorption of oral medications due to delayed gastric emptying, including oral contraceptives. Women of childbearing potential should use additional contraception for 4 weeks after initiation and after each dose increase. Tirzepatide should be avoided during pregnancy and breastfeeding, with appropriate preconception discontinuation intervals as advised in the SmPC.
Patients with Crohn's disease considering Mounjaro should be aware of several potential risks and side effects that may be particularly relevant to their condition. The most common adverse effects of tirzepatide are gastrointestinal in nature, including:
Nausea and vomiting: These are reported in a significant proportion of patients, especially during the initial weeks of treatment.
Diarrhoea: This can be problematic for Crohn's patients, who may already experience frequent loose stools.
Abdominal pain and bloating: These symptoms may mimic or worsen existing Crohn's-related discomfort.
Constipation: Although less common, this can occur and may be concerning in patients with stricturing disease.
For individuals with Crohn's disease, these side effects may complicate symptom assessment and make it difficult to determine whether gastrointestinal symptoms are due to the medication, a disease flare, or both. This could delay appropriate escalation of IBD therapy if a flare is mistakenly attributed to Mounjaro.
Another consideration is the risk of dehydration, particularly if vomiting or diarrhoea is severe. Crohn's patients, especially those with active disease or previous bowel resections, may already be at increased risk of fluid and electrolyte imbalances. Adequate hydration and monitoring of renal function are therefore important, as dehydration can lead to acute kidney injury.
There is also a concern regarding pancreatitis, a rare but serious adverse effect associated with GLP-1 receptor agonists. While the absolute risk is low, patients with a history of pancreatitis or gallstones should be counselled accordingly. Tirzepatide may increase the risk of gallbladder disease (cholelithiasis, cholecystitis); patients should report symptoms such as right upper quadrant pain, fever, or jaundice.
The SmPC contains a special warning regarding thyroid C-cell tumours observed in animal studies, though the relevance to humans remains uncertain. Patients should be advised to report symptoms such as a lump in the neck, hoarseness, or difficulty swallowing.
When used with insulin or sulfonylureas, there is an increased risk of hypoglycaemia; dose reductions of these agents may be required when initiating tirzepatide.
Before starting Mounjaro, patients with Crohn's disease should have a thorough discussion with their GP, endocrinologist, or gastroenterologist to ensure the treatment is appropriate and safe. Key topics to cover include:
Current Crohn's disease activity: Is your Crohn's well-controlled or are you experiencing active symptoms? Patients in remission are more likely to tolerate Mounjaro without confusion between drug side effects and disease flares.
Previous gastrointestinal surgery: While subcutaneous tirzepatide absorption is not affected by bowel resections, patients with strictures may be at higher risk of obstruction due to reduced gastric emptying. Additionally, tirzepatide may affect the timing and absorption of oral medicines due to delayed gastric emptying.
Current medications: Provide a complete list of all medications, including immunosuppressants, biologics, and corticosteroids. If you take time-critical or narrow therapeutic index oral drugs, discuss potential absorption issues. If you use insulin or sulfonylureas, dose adjustments may be needed to prevent hypoglycaemia.
Contraception and pregnancy planning: Tirzepatide reduces exposure to oral contraceptives; additional contraception is recommended for 4 weeks after initiation and after each dose increase. The medication should be avoided during pregnancy and breastfeeding, with appropriate preconception discontinuation intervals as per the SmPC.
History of pancreatitis, gallstones, or gallbladder disease: These conditions may increase the risk of adverse events with GLP-1-based therapies.
Symptoms to monitor: Clarify which symptoms should prompt urgent medical review, such as severe abdominal pain, persistent vomiting, signs of dehydration, or blood in the stool.
Monitoring plan: Agree on a schedule for follow-up appointments, blood tests (including HbA1c, renal function, and inflammatory markers), and faecal calprotectin if appropriate.
Patients should also discuss their treatment goals—whether the primary aim is glycaemic control, weight loss, or both—and weigh these against the potential for gastrointestinal side effects. If Mounjaro is initiated, a low starting dose with gradual titration is advisable, and patients should be encouraged to report any new or worsening symptoms promptly. Maintaining open communication between all members of the healthcare team is essential to optimise outcomes and ensure patient safety.
Patients should be advised to report suspected side effects via the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk or via the Yellow Card app).
Mounjaro is not specifically contraindicated in Crohn's disease, but its gastrointestinal side effects may complicate symptom monitoring. Patients with well-controlled disease in remission are more suitable candidates, and prescribing should involve close collaboration between gastroenterology and prescribing teams.
The most relevant side effects are nausea, vomiting, diarrhoea, and abdominal pain, which may overlap with Crohn's symptoms and make it difficult to distinguish between medication effects and disease flares. Dehydration risk is also increased, particularly in patients with active disease.
No, you should continue your Crohn's disease treatment as prescribed. Discuss all current medications with your doctor, as tirzepatide may affect absorption of oral medicines due to delayed gastric emptying, and dose adjustments may be needed for insulin or sulfonylureas if used for diabetes.
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