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 potential side effects of Mounjaro (tirzepatide), though they are not among the most common effects reported in clinical trials. If you experience persistent or severe heartburn while taking this prescription-only weight management injection, it's important to understand why it happens and when to contact your GP. This guide explains the connection between Mounjaro and heartburn, how to manage it, and what steps to take if symptoms become troublesome.
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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 Mounjaro May Cause Heartburn
Mounjaro works as a dual GIP and GLP-1 receptor agonist, activating natural hormone pathways that regulate appetite and blood sugar. One of these effects is slowing gastric emptying — how quickly food moves from your stomach into your small intestine. When food stays in your stomach longer, it can increase stomach acid production and pressure, which may trigger acid reflux or heartburn symptoms.
Additionally, Mounjaro can affect the muscles in your oesophagus and lower oesophageal sphincter (the valve that prevents stomach acid from rising). Some people experience indigestion or dyspepsia as a common side effect, which may include heartburn. This is more likely when you first start the tirzepatide dose or during dose escalation, as your body adjusts to the medication.
Importantly, heartburn is different from the nausea or stomach pain that are very common with Mounjaro — heartburn is listed as a possible but less frequent effect.
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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.
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Managing Heartburn While Taking Mounjaro
If you develop heartburn on Mounjaro, several practical strategies may help: eat smaller, more frequent meals rather than large portions; avoid trigger foods like fatty, spicy, or acidic foods; do not eat close to bedtime; stay upright for at least 3 hours after eating; and stay well hydrated. Many people find that heartburn improves naturally as their body adapts to the medication over the first few weeks.
Over-the-counter antacids like calcium carbonate or alginates may provide relief, though you should check with your GP or pharmacist before taking any new medication alongside Mounjaro. Prescription-strength options like proton pump inhibitors (PPIs) are also available if over-the-counter treatments are not sufficient. Always inform your prescriber about persistent heartburn so they can assess whether it requires additional treatment or whether dose adjustment might help.
When to Contact Your GPWhile occasional heartburn is uncomfortable but not usually serious, contact your GP if: heartburn is severe or persistent and does not improve with lifestyle changes or over-the-counter antacids; you develop difficulty swallowing or chest pain (which could indicate a more serious condition); you experience heartburn alongside vomiting or signs of bleeding; or if heartburn is affecting your quality of life and willingness to continue the medication.
Your GP can assess whether the heartburn is related to Mounjaro or another cause, recommend appropriate treatment, and discuss whether continuing at your current dose or adjusting your treatment plan is appropriate. Never stop taking Mounjaro without medical guidance — your prescriber needs to manage any changes safely.
- 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.
Is heartburn a common side effect of Mounjaro?
Heartburn and indigestion are listed as common side effects in the prescribing information, affecting up to 1 in 10 people. However, they are less frequent than nausea, diarrhoea, or constipation. Many people taking Mounjaro do not experience heartburn at all, and symptoms often improve over time as your body adjusts.
Can I take antacids while taking Mounjaro?
Yes, over-the-counter antacids like calcium carbonate or alginates are generally safe to use with Mounjaro. However, always inform your GP or pharmacist that you are taking Mounjaro before starting any new medication. If over-the-counter options are not enough, your GP can prescribe stronger treatments like proton pump inhibitors.
Why does Mounjaro cause heartburn more than Wegovy?
Mounjaro is a dual GIP and GLP-1 agonist, whereas Wegovy (semaglutide) is a GLP-1 agonist only. The additional GIP mechanism in tirzepatide may contribute to slightly different gastrointestinal effects. Both medications can cause heartburn, but individual responses vary. Your prescriber can discuss which option may be better for you.
Will heartburn go away as I continue taking Mounjaro?
For many people, heartburn and other gastrointestinal side effects improve within the first few weeks as the body adapts to the medication. However, some people experience persistent symptoms. If heartburn continues after several weeks, discuss it with your GP — they may recommend treatment or dose adjustments.
Should I stop taking Mounjaro if I get heartburn?
Do not stop Mounjaro without consulting your prescriber. Heartburn is manageable with lifestyle changes and medication. Your GP can assess the severity, recommend treatment options, and help you decide whether to continue, adjust the dose, or explore alternative medications. Stopping suddenly without guidance is not recommended.
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