Mounjaro (tirzepatide) is a once-weekly injection authorised in the UK for treating type 2 diabetes mellitus. As a dual GIP and GLP-1 receptor agonist, it works by slowing gastric emptying, enhancing insulin secretion, and promoting satiety. Whilst gastrointestinal side effects such as nausea, dyspepsia, and abdominal discomfort are commonly reported, some patients may experience heartburn or reflux symptoms. Understanding the relationship between Mounjaro and heartburn, alongside practical management strategies, can help patients optimise their treatment whilst maintaining comfort and safety. This article explores how Mounjaro may influence reflux symptoms and when to seek medical advice.

What Is Mounjaro and How Does It Work?

Mounjaro (tirzepatide) is a prescription medicine authorised in the UK for the treatment of type 2 diabetes mellitus. It is administered as a once-weekly subcutaneous injection and belongs to a novel class of medicines 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 that play crucial roles in glucose regulation and appetite control. By activating both GIP and GLP-1 receptors, tirzepatide enhances insulin secretion in a glucose-dependent manner, suppresses inappropriate glucagon release, slows gastric emptying, and promotes satiety. This dual action results in improved glycaemic control and significant weight reduction in clinical trials.

The slowing of gastric emptying is particularly relevant when considering gastrointestinal side effects. By delaying the passage of food from the stomach into the small intestine, Mounjaro helps regulate post-meal blood glucose levels and contributes to feelings of fullness. However, this same mechanism can influence digestive processes and may contribute to gastrointestinal symptoms in some patients. Importantly, this delayed gastric emptying may affect the absorption of oral medicines, including oral contraceptives. Additional contraceptive precautions are recommended for 4 weeks after starting treatment and after each dose increase.

Mounjaro is typically initiated at a low dose (2.5 mg once weekly for 4 weeks) and gradually increased at intervals of at least 4 weeks (by 2.5 mg increments) to minimise side effects and allow the body to adjust, up to a maximum of 15 mg weekly. The National Institute for Health and Care Excellence (NICE) provides specific guidance on NHS eligibility criteria for tirzepatide in both diabetes management and, more recently, for weight management in adults with obesity within specialist services.

Can Mounjaro Cause Heartburn?

Heartburn, medically termed gastro-oesophageal reflux, is characterised by a burning sensation in the chest caused by stomach acid flowing back into the oesophagus. While heartburn is not specifically listed among the most common adverse effects of Mounjaro, gastrointestinal symptoms are frequently reported with GLP-1 receptor agonists and dual agonists like tirzepatide.

The most commonly reported gastrointestinal side effects of Mounjaro include nausea, diarrhoea, vomiting, constipation, abdominal pain, and dyspepsia (indigestion). In clinical trials, these effects were generally mild to moderate in severity and tended to decrease over time as patients continued treatment. Dyspepsia, which can encompass symptoms similar to heartburn including reflux, was reported as a common side effect in clinical trials.

While heartburn is not specifically named in the Summary of Product Characteristics, the medication's effect on gastric emptying may theoretically influence reflux symptoms in susceptible individuals. When the stomach empties more slowly, food and gastric contents remain in the stomach for longer periods, which could potentially increase intra-gastric pressure and the likelihood of reflux in some patients.

It is important to note that many individuals taking Mounjaro for diabetes may have pre-existing risk factors for gastro-oesophageal reflux disease (GORD), including obesity, dietary habits, and hiatus hernia. Weight loss achieved through Mounjaro treatment may actually improve reflux symptoms over time in many patients, as excess abdominal weight is a known contributor to GORD. If you experience new or worsening heartburn after starting Mounjaro, it is essential to discuss this with your healthcare provider to determine the underlying cause and appropriate management.

For a complete list of possible side effects and their frequencies, please refer to the Patient Information Leaflet that comes with your medication.

Managing Heartburn While Taking Mounjaro

If you experience heartburn whilst taking Mounjaro, several practical strategies can help manage symptoms effectively without necessarily discontinuing your medication. These approaches focus on lifestyle modifications, dietary adjustments, and appropriate use of over-the-counter remedies when needed.

Dietary and lifestyle modifications form the cornerstone of heartburn management:

• Eat smaller, more frequent meals rather than large portions, which can reduce gastric distension and pressure

• Avoid trigger foods such as spicy dishes, citrus fruits, tomatoes, chocolate, caffeine, and fatty or fried foods

• Remain upright for at least two to three hours after eating; avoid lying down immediately after meals

• Elevate the head of your bed by 15–20 cm using blocks or a wedge pillow to reduce nocturnal reflux

• Avoid tight-fitting clothing around the abdomen, which can increase intra-abdominal pressure

• Limit alcohol consumption and avoid smoking, both of which can exacerbate reflux symptoms

Over-the-counter antacids containing aluminium hydroxide, magnesium hydroxide, or calcium carbonate can provide rapid, short-term relief by neutralising stomach acid. These are generally safe to use alongside Mounjaro.

If lifestyle measures prove insufficient, your GP may recommend acid-suppressing medications such as proton pump inhibitors (PPIs) like omeprazole or lansoprazole, or histamine-2 receptor antagonists (H2RAs) such as famotidine. These can be used safely with Mounjaro and may provide more sustained symptom control for persistent heartburn.

Your GP may also review your other medications, as some can worsen reflux symptoms, including non-steroidal anti-inflammatory drugs (NSAIDs), certain calcium channel blockers, bisphosphonates, and oral steroids.

If you suspect your heartburn is related to Mounjaro, discuss this with your healthcare provider. They can assess whether the benefits of continuing treatment outweigh the symptoms you're experiencing and may consider adjustments to your treatment plan.

When to Seek Medical Advice About Heartburn on Mounjaro

While mild, occasional heartburn can often be managed with lifestyle modifications and over-the-counter remedies, certain symptoms warrant prompt medical evaluation. It is important to recognise when heartburn may indicate a more serious condition or when professional guidance is needed to optimise your treatment.

Contact your GP or healthcare provider if you experience:

• Persistent or worsening heartburn despite lifestyle changes and antacid use

• Difficulty or pain when swallowing (dysphagia or odynophagia), which may indicate oesophageal inflammation or stricture

• Unintentional weight loss beyond what is expected from Mounjaro treatment

• Persistent nausea or vomiting that prevents adequate food or fluid intake

• Signs of gastrointestinal bleeding, including black, tarry stools or vomiting blood or coffee-ground material

• Iron-deficiency anaemia (symptoms may include fatigue, weakness, pale skin)

• Severe abdominal pain, particularly if persistent or radiating to the back, which could indicate pancreatitis (a rare but serious side effect of GLP-1 receptor agonists)

• Right upper abdominal pain, fever or jaundice, which could indicate gallbladder problems (known to occur with GLP-1/GIP agents)

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

• Chest pain that is severe, crushing, or radiating to the arm, neck, or jaw, as this may indicate a cardiac event rather than simple heartburn

• Severe difficulty breathing or sensation of choking

• Persistent vomiting with inability to keep down fluids, leading to dehydration

Your healthcare provider can assess whether your symptoms are related to Mounjaro, represent an underlying condition such as GORD or peptic ulcer disease, or require investigation. NICE guidance (CG184) recommends that patients with alarm symptoms (dysphagia, weight loss, persistent vomiting, evidence of gastrointestinal bleeding, or iron-deficiency anaemia) should be referred for urgent endoscopic evaluation to exclude serious pathology. For patients aged 55 and over with unexplained weight loss and dyspepsia, urgent referral should be considered under suspected cancer guidelines (NG12).

If you believe you have experienced a side effect from Mounjaro, you can report this through the Yellow Card Scheme at yellowcard.mhra.gov.uk or via the Yellow Card app. Never discontinue Mounjaro without medical advice, as this may affect your diabetes control.

Frequently Asked Questions