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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How Long Do Sulphur Burps Last on Mounjaro?
Sulphur burps (also called rotten egg burps) are a recognised side effect of Mounjaro (tirzepatide), the GLP-1 and GIP receptor agonist injection used for weight management in the UK. Most people who experience them find they resolve within 2–4 weeks as their body adjusts to the medication. However, timing varies between individuals depending on the dose and personal tolerance. If sulphur burps persist beyond a month or cause significant distress, your GP or prescriber can discuss management options with you.
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Calculate Your BMI Instantly
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.
What Causes Sulphur Burps on Mounjaro?
Sulphur burps occur because Mounjaro slows gastric emptying — the rate at which food moves from your stomach into the small intestine. When food stays in the stomach longer, bacteria ferment undigested carbohydrates, producing hydrogen sulphide gas, which creates that distinctive rotten egg smell.
This is not a sign that Mounjaro is harming you — it's a normal pharmacological effect as your digestive system adapts to the medication. The effect typically decreases over time as your body becomes accustomed to the tirzepatide dose. Most people notice sulphur burps are worst in the first 1–2 weeks after starting Mounjaro or increasing their dose, then gradually improve.
Other digestive changes that sometimes accompany sulphur burps include bloating, constipation, or diarrhoea — these are common early side effects that usually settle within the first month.
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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 Sulphur Burps and When to Speak to Your GP
If you're experiencing sulphur burps, simple dietary changes can help: eat smaller, more frequent meals; choose easily digestible foods like chicken, fish, and vegetables; avoid high-fat foods and carbonated drinks; and stay hydrated with water. Some people find that eating slowly and chewing thoroughly reduces the frequency.
If sulphur burps persist beyond 4 weeks, are severe, or significantly affect your quality of life, contact your GP or the prescriber who issued your Mounjaro prescription. They may adjust your dose timing, suggest additional management strategies, or review whether Mounjaro remains the right choice for you. Always report persistent or bothersome side effects — they're important clinical information that helps your healthcare team support you effectively.
- 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 sign Mounjaro is not working?
No. Sulphur burps are a side effect caused by slower gastric emptying, not a sign of treatment failure. They're separate from weight loss efficacy. Most people still experience significant weight loss even when sulphur burps occur. If you have concerns about whether Mounjaro is working for you, discuss this with your prescriber rather than stopping the medication.
Can I prevent sulphur burps before they start?
There's no assured prevention, but eating smaller meals, avoiding high-fat foods, and staying hydrated from the start may reduce their severity. Some people experience them mildly or not at all. Taking Mounjaro as prescribed and following your prescriber's guidance on dose titration helps your body adjust gradually.
Do sulphur burps mean I should stop taking Mounjaro?
Not necessarily. Most people's sulphur burps resolve within 2–4 weeks as their body adapts. However, if they're severely affecting your wellbeing or don't improve after a month, speak to your GP. They can discuss whether to continue, adjust your dose, or explore alternatives like Wegovy, which may cause different side effects.
How does Mounjaro dose titration affect sulphur burps?
Sulphur burps often intensify temporarily when you increase your tirzepatide dose because your digestive system needs to readjust. They typically settle again within 2–4 weeks at the new dose. Your prescriber spaces dose increases at least 4 weeks apart to allow time for adaptation.
Should I use our GLP-1 calculator to estimate my potential side effects?
Our free weight loss calculator helps you project potential weight loss outcomes with Mounjaro at different doses, but individual side effects vary significantly and can't be predicted in advance. Use it to understand realistic weight loss expectations, then discuss side effect tolerance with your prescriber when planning your treatment.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.