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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Sulphur Burps on Mounjaro — What You Need to Know
Sulphur burps (rotten egg-like belching) are a reported side effect experienced by some people taking Mounjaro (tirzepatide) in the UK. Whilst not listed as a common side effect in the official prescribing information, anecdotal reports suggest this can occur, particularly during the early weeks of treatment or after dose increases. This guide explains what causes them, how long they typically last, and when to seek advice from your GP or healthcare provider.
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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.
Why Sulphur Burps Occur on Mounjaro
Sulphur burps are thought to occur due to how Mounjaro affects your digestive system. As a dual GIP and GLP-1 receptor agonist, Mounjaro slows gastric emptying—the speed at which food leaves your stomach. This slower digestion can lead to bacterial fermentation in the digestive tract, which may produce hydrogen sulphide gas, causing the characteristic rotten egg smell.
Additionally, Mounjaro may reduce stomach acid production, which normally helps break down food and control bacteria. With less acid, bacterial overgrowth becomes more likely, further increasing gas production. The effect is usually temporary as your body adjusts to the medication over the first few weeks of treatment.
Other common digestive side effects—nausea, constipation, and diarrhoea—often occur alongside sulphur burps, suggesting that digestive changes are a normal part of how the medication works.
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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 Sulphur Burps and When to Seek Help
Most people find sulphur burps improve within 2–4 weeks as their body adapts to Mounjaro. Practical steps may help: eat smaller, more frequent meals; avoid fatty or heavy foods; stay hydrated; chew food thoroughly; and consider ginger or peppermint tea, which may support digestion. If you're on a Mounjaro KwikPen prescription, your prescriber may adjust your dose schedule if side effects are severe.
Contact your GP or prescriber if sulphur burps persist beyond 4 weeks, are accompanied by severe stomach pain, or significantly affect your quality of life. These symptoms alone rarely indicate a serious issue, but your healthcare provider can rule out other causes and discuss dose adjustments or alternative weight loss options if needed.
- 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.
Are sulphur burps a common side effect of Mounjaro?
Sulphur burps are not listed as a common side effect in Mounjaro's official information, but anecdotal reports from UK users suggest they do occur in some people, particularly in the first few weeks. They are usually temporary as your digestive system adjusts to the medication.
How long do sulphur burps last on Mounjaro?
Most people report that sulphur burps improve within 2–4 weeks of starting treatment or after a dose increase. If they persist beyond 4 weeks, contact your GP or prescriber for personalised advice.
Can I prevent sulphur burps on Mounjaro?
Eating smaller meals, avoiding fatty foods, staying hydrated, and chewing thoroughly may help reduce sulphur burps. There is no assured prevention, but these dietary adjustments support healthy digestion whilst taking any GLP-1 or GIP/GLP-1 medication like Mounjaro.
Should I contact my GP about sulphur burps?
Sulphur burps alone are not usually concerning. However, contact your GP if they persist beyond 4 weeks, are accompanied by severe abdominal pain, or significantly impact your wellbeing. Your prescriber can assess whether a dose adjustment is appropriate.
Are sulphur burps a sign that Mounjaro isn't working?
No. Sulphur burps are a digestive side effect, not an indicator of treatment efficacy. If you have concerns about weight loss progress, use our free GLP-1 weight loss calculator to set realistic expectations, then discuss your results with your prescriber.
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