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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Why Do I Get Sulphur Burps on Mounjaro?
Sulphur burps (also called rotten egg burps) are a known side effect of Mounjaro and other GLP-1 medications. They occur because tirzepatide and similar medications slow how quickly food moves through your stomach, allowing more time for bacterial fermentation. This produces hydrogen sulphide gas, which creates that distinctive sulphur smell. The same mechanism affects both Mounjaro and Wegovy, though the frequency and severity vary between individuals. Understanding why this happens and how it compares between medications can help you manage this common side effect.
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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 and Wegovy Cause Sulphur Burps
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) slow gastric emptying—the rate at which food leaves your stomach. This is actually part of how they help with weight loss, as slower digestion supports longer feelings of fullness. However, this delayed emptying creates an environment where food sits longer in your stomach, allowing bacteria to ferment undigested material and produce hydrogen sulphide gas.
Mounjaro works via a dual GIP and GLP-1 mechanism, whilst Wegovy acts through GLP-1 only. Clinical trials show both cause similar gastrointestinal side effects, including sulphur burps, though individual experiences vary. The SURMOUNT trial (Mounjaro) and STEP trials (Wegovy) reported nausea, diarrhoea, and stomach discomfort as very common side effects, with sulphur burps mentioned by patients on both medications. Starting at lower doses and titrating gradually—as your prescriber recommends—typically reduces the severity of this effect over time.
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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.
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Managing Sulphur Burps and When to Seek Advice
Sulphur burps usually improve within the first few weeks as your body adjusts to the medication. Several strategies may help: eat smaller, more frequent meals; avoid high-fat or high-fibre foods that ferment easily; stay hydrated; and take your time eating. Some people find that chewing food thoroughly and eating slowly reduces symptoms. If sulphur burps are severe or persistent after 4–6 weeks, contact your prescriber—they may adjust your dose or suggest short-term dietary changes. Never stop your medication without medical guidance. Both medications require a prescription and clinical assessment, and your prescriber can advise whether continuing at your current dose is appropriate or whether adjusting your dose titration schedule might help.
- 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 more common on Mounjaro or Wegovy?
Clinical trial data shows both medications cause similar rates of gastrointestinal side effects, including sulphur burps. Individual experiences vary based on dose, diet, and how quickly your body adjusts. Neither medication assures this side effect—some people experience it mildly or not at all. Your prescriber can discuss what to expect based on your personal health history.
How long do sulphur burps last on Mounjaro?
Most people find sulphur burps improve significantly within 2–4 weeks as their body adjusts to the medication. If you're still experiencing severe symptoms after 6 weeks, contact your GP or prescriber. Adjusting your diet—smaller meals, less fatty food—often helps whilst your body adapts.
Can I reduce sulphur burps by changing my diet?
Yes. Avoid high-fat, high-fibre, and heavily processed foods that ferment easily. Eat smaller meals more frequently, chew thoroughly, and drink plenty of water. Some people find that ginger tea or peppermint tea helps. Keep a food diary to identify which foods trigger symptoms worst.
Should I stop taking Mounjaro if I get sulphur burps?
No—never stop your medication without speaking to your prescriber first. Sulphur burps are a known side effect that typically improves with time. If they're severe or affecting your quality of life, your GP can advise whether dose adjustment or temporary dietary changes might help. They may also discuss whether continuing is right for you personally.
Is there a difference between Mounjaro and Wegovy for this side effect?
Both medications slow gastric emptying and can cause sulphur burps. Mounjaro is a dual GIP+GLP-1 agonist, whilst Wegovy is GLP-1 only, but clinical data shows similar gastrointestinal side effect profiles. Individual tolerance varies more than the medication itself—your prescriber can assess which is more suitable for you based on your health history.
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