The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
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Does Mounjaro Cause Heartburn?
Heartburn and acid reflux are common side effects reported by people taking Mounjaro (tirzepatide) for weight management. This dual GIP and GLP-1 receptor agonist can slow gastric emptying and affect digestion, which may trigger or worsen heartburn in some users. Understanding what to expect, when to seek help, and how to manage symptoms can help you get the most from your treatment. This guide covers the evidence, practical management strategies, and when to contact your GP or prescriber.
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Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
How Common Is Heartburn on Mounjaro?
Heartburn and indigestion are common side effects of Mounjaro, affecting a significant proportion of users during dose escalation. Clinical data suggests that up to 1 in 10 people may experience indigestion (dyspepsia) or acid reflux (gastro-oesophageal reflux disease, GORD) when taking tirzepatide. The risk tends to be highest when starting the medication or increasing your dose, and many people find symptoms improve over time as their body adjusts. Heartburn typically occurs because Mounjaro slows how quickly food leaves your stomach — this delayed gastric emptying can allow stomach acid to irritate the oesophagus more easily. Unlike some side effects that fade quickly, heartburn may persist for several weeks or months, though it often becomes manageable with lifestyle adjustments and over-the-counter remedies. Severity varies widely between individuals — some experience mild discomfort after meals, while others report more troublesome symptoms.
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How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Managing Heartburn While on Mounjaro
If you develop heartburn on Mounjaro, several practical steps can help reduce symptoms. Eating smaller, more frequent meals rather than large meals can ease pressure on your stomach. Avoid foods that trigger acid reflux — common culprits include fatty foods, spicy meals, chocolate, caffeine, and acidic drinks. Eating slowly and chewing thoroughly gives your stomach more time to digest. Staying upright for at least two to three hours after eating helps keep stomach acid where it belongs. You can also try raising the head of your bed slightly or taking an antacid like ranitidine or omeprazole before meals — speak to your GP or pharmacist about which option suits you. If heartburn persists despite these measures, inform your prescriber, as they may adjust your Mounjaro dose or explore other management options tailored to your individual situation.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Should I stop taking Mounjaro if I get heartburn?
No — you should not stop without medical guidance. Heartburn is a known side effect that often improves with time and lifestyle changes. Speak to your prescriber or GP first. They may suggest management strategies, temporary dose adjustment, or medication to ease symptoms. Stopping abruptly is not recommended.
Is heartburn a sign Mounjaro is not right for me?
Not necessarily. Heartburn is a common adjustment side effect, especially during dose escalation, and does not mean you cannot take Mounjaro long-term. Many people experience initial heartburn that resolves within weeks. Your prescriber can assess whether it is manageable or whether an alternative treatment might suit you better.
Can I take antacids with Mounjaro?
Yes, over-the-counter antacids like ranitidine, omeprazole, or calcium carbonate are generally safe to use alongside Mounjaro. However, tell your GP or prescriber before starting any new medication, as some drugs may interact or affect how well Mounjaro works. Your pharmacist can recommend the most suitable option for you.
Does heartburn happen with all GLP-1 or tirzepatide doses?
Heartburn can occur at any dose of Mounjaro, but it is often more noticeable during the first few weeks and when doses increase. Some people experience it consistently, while others report it only at certain doses or not at all. Individual responses vary — your prescriber can help identify patterns specific to you.
When should I contact my GP about Mounjaro heartburn?
Contact your GP if heartburn is severe, persistent despite management efforts, accompanied by chest pain, difficulty swallowing, or vomiting. These could indicate a more serious condition like gastro-oesophageal reflux disease or pancreatitis. Seek urgent medical attention if you experience severe abdominal pain. Always report ongoing side effects to your prescriber during your reviews.
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