Sulphur Burps and Diarrhoea on Mounjaro: Causes and Management

Sulphur burps and diarrhoea are very common gastrointestinal side effects experienced by people taking Mounjaro (tirzepatide) for type 2 diabetes or weight management. These symptoms occur because Mounjaro slows gastric emptying and alters digestive processes as part of its mechanism of action. Sulphurous burps—often described as having a 'rotten egg' smell—result from hydrogen sulphide gas production in the digestive system, whilst diarrhoea affects more than 10% of patients according to clinical trial data. Whilst uncomfortable, these symptoms typically improve over time as the body adjusts to treatment. This article provides evidence-based guidance on managing these side effects effectively and recognising when medical review is needed.

Understanding Sulphur Burps and Diarrhoea with Mounjaro

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. For weight management, NICE guidance specifies that tirzepatide should be prescribed within specialist weight management services, for people meeting specific BMI criteria with weight-related comorbidities, and as part of a time-limited treatment plan.

As a glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) receptor agonist, Mounjaro works by mimicking natural gut hormones that regulate blood sugar and appetite.

According to the MHRA/EMC Summary of Product Characteristics (SmPC), gastrointestinal adverse effects are very common with Mounjaro. Diarrhoea, nausea, vomiting and decreased appetite occur in ≥10% of patients, while eructation (belching) can also occur. Some people notice a sulphurous odour to their burps—often described as a 'rotten egg' smell—which is caused by hydrogen sulphide gas.

These symptoms can range from mild and transient to more persistent and troublesome, occasionally affecting treatment adherence and quality of life. Gastrointestinal effects typically occur during the initial weeks of treatment or following dose escalation, with many improving as the body adjusts to the medication.

It is important to recognise that whilst these symptoms can be uncomfortable, they do not necessarily indicate a serious medical problem. However, persistent or severe symptoms warrant medical review to exclude other causes and to ensure appropriate management. This article provides evidence-based guidance on why these symptoms occur, how to manage them effectively, and when to seek professional medical advice.

Why Mounjaro Causes Digestive Side Effects

The gastrointestinal side effects associated with Mounjaro are directly related to its mechanism of action. Tirzepatide activates both GLP-1 and GIP receptors in the gut, pancreas, and brain. This dual action slows gastric emptying—the rate at which food moves from the stomach into the small intestine—which contributes to increased satiety and improved glycaemic control. However, this delayed gastric emptying can lead to feelings of fullness, nausea, and altered digestive patterns.

Gastrointestinal symptoms such as nausea, vomiting, diarrhoea, and belching are recognised class effects of GLP-1-based therapies. According to the MHRA/EMC SmPC and European Medicines Agency (EMA) assessment report, these effects are most pronounced during dose escalation phases.

Eructation (belching) with a sulphurous odour may occur when patients take Mounjaro. This happens when hydrogen sulphide gas is produced in the digestive system and expelled through burping. Certain foods high in sulphur compounds—such as eggs, red meat, cruciferous vegetables, and some dairy products—may contribute to this effect in susceptible individuals.

Diarrhoea is a very common side effect of Mounjaro, occurring in ≥10% of patients according to clinical trials. While the exact mechanism is not fully established, it is part of the spectrum of gastrointestinal effects seen with GLP-1 receptor agonists.

The incidence of these side effects is typically highest during the initial titration phase when the body is adjusting to the medication. Most cases are mild to moderate in severity and tend to diminish over time as tolerance develops, though some patients may experience persistent symptoms requiring management strategies.

Managing Sulphur Burps and Diarrhoea on Mounjaro

Effective management of gastrointestinal symptoms whilst taking Mounjaro involves a combination of lifestyle modifications, dietary adjustments, and symptomatic relief measures. Patients should be reassured that these symptoms often improve with continued treatment as the body adapts to the medication.

For sulphurous burps and belching, consider the following strategies:

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

• Chew food thoroughly and eat slowly to aid digestion and reduce air swallowing

• Avoid lying down immediately after eating; remain upright for at least 2–3 hours post-meal

• Stay well hydrated with water throughout the day

• Consider over-the-counter products containing simeticone or alginate that may help with bloating or acid reflux (ask your pharmacist for advice)

For diarrhoea management:

• Maintain adequate hydration with water, clear broths, or oral rehydration solutions to replace lost fluids and electrolytes

• Avoid caffeine and alcohol, which can worsen diarrhoea

• Consider probiotics, which may help some people, though evidence for their effectiveness in medication-induced diarrhoea is limited

• Use anti-diarrhoeal medications such as loperamide cautiously and only after consulting your GP or pharmacist

• Keep a symptom diary to identify potential dietary triggers

It is essential to continue taking Mounjaro as prescribed unless advised otherwise by your healthcare provider. Abruptly stopping the medication can affect blood sugar control in patients with diabetes. If symptoms are severe or persistent beyond the first few weeks, discuss dose adjustment options with your prescribing clinician, as a slower titration schedule may improve tolerability.

If pancreatitis is suspected (severe abdominal pain, often radiating to the back), stop taking Mounjaro immediately and seek urgent medical advice. For urgent but non-emergency advice when your GP is unavailable, contact NHS 111.

When to Contact Your GP About Mounjaro Side Effects

Whilst mild gastrointestinal symptoms are common and often self-limiting, certain warning signs require prompt medical evaluation. Patients should contact their GP or healthcare provider if they experience:

• Severe or persistent diarrhoea lasting more than 48 hours, particularly if accompanied by signs of dehydration (dizziness, reduced urination, dry mouth, confusion)

• Blood in stools or black, tarry stools, which may indicate gastrointestinal bleeding

• Severe abdominal pain, especially if constant or worsening, which could suggest pancreatitis—a serious adverse effect that has been reported with GLP-1-based therapies. If pancreatitis is suspected, stop taking Mounjaro until this has been excluded

• Right upper abdominal pain, fever, or yellowing of the skin/eyes, which could indicate gallbladder disease—an adverse effect associated with GLP-1-based therapies

• Persistent vomiting that prevents adequate fluid or medication intake

• Signs of dehydration including decreased urine output, extreme thirst, or lightheadedness

• Unexplained weight loss beyond expected therapeutic effects

• Symptoms of hypoglycaemia (low blood sugar) such as trembling, sweating, confusion, or palpitations, particularly if taking Mounjaro alongside insulin or sulphonylureas

Seek immediate medical attention (call 999 or attend A&E) if you experience:

• Severe, unrelenting abdominal pain radiating to the back

• Signs of severe allergic reaction (anaphylaxis): difficulty breathing, facial swelling, or widespread rash

• Symptoms of diabetic ketoacidosis in insulin-treated patients: excessive thirst, frequent urination, nausea, vomiting, abdominal pain, confusion, or fruity-smelling breath (note: do not abruptly reduce insulin doses without medical supervision)

For urgent but non-emergency advice when your GP is unavailable, contact NHS 111.

Your GP can assess whether symptoms are related to Mounjaro or indicate another underlying condition requiring investigation. They may recommend temporary dose reduction, additional investigations, or referral to specialist services if appropriate. Never discontinue Mounjaro without medical guidance, particularly if prescribed for diabetes management.

Suspected adverse reactions to Mounjaro should be reported via the MHRA Yellow Card scheme (yellowcard.mhra.gov.uk).

Dietary Changes to Reduce Digestive Symptoms

Strategic dietary modifications can significantly reduce the frequency and severity of digestive symptoms whilst taking Mounjaro. These changes work by reducing the burden on the slowed digestive system and minimising foods that contribute to gas production or loose stools.

Foods to consider limiting (particularly during the initial treatment phase):

• Foods high in sulphur compounds that may contribute to malodorous gas: eggs, red meat, poultry, cruciferous vegetables (broccoli, cauliflower, Brussels sprouts, cabbage), garlic, onions

• High-fat foods: fried foods, fatty cuts of meat, full-fat dairy, and rich sauces, which delay gastric emptying further

• Spicy or heavily seasoned foods, which may irritate the digestive tract

• Carbonated beverages, which introduce additional gas

• Artificial sweeteners (sorbitol, mannitol, xylitol), which can have a laxative effect

Foods that may be better tolerated:

• Lean proteins: fish, skinless chicken breast, tofu

• Low-gas vegetables: courgettes, carrots, green beans, and leafy greens

• Easily digestible carbohydrates: white rice, pasta, potatoes, and white bread (during acute symptoms)

• Plain, starchy foods such as bananas, rice, toast, and potatoes during episodes of diarrhoea

• Ginger tea, which may help with nausea (peppermint tea may help some people but can worsen reflux in others)

Practical eating strategies:

• Eat smaller portions spread across 5–6 meals daily rather than three large meals

• Allow adequate time between eating and lying down (minimum 2–3 hours)

• Introduce new foods gradually to identify personal triggers

• Maintain a food and symptom diary to establish patterns

• Consider soluble fibre (e.g., oats, psyllium) once acute diarrhoea resolves

It's important to note that individual responses to foods vary considerably. Rather than eliminating multiple food groups long-term, consider a systematic approach of temporarily reducing potential trigger foods and gradually reintroducing them to identify your specific sensitivities.

Consider requesting a referral to a registered dietitian through your GP, particularly if you have diabetes or other nutritional considerations. NICE guidance emphasises the importance of individualised dietary advice for patients taking GLP-1 receptor agonists to optimise both therapeutic outcomes and quality of life whilst minimising adverse effects.

Frequently Asked Questions