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 Does Mounjaro Cause Sulphur Burps?
Sulphur burps (also called rotten egg burps) are a side effect some people experience when taking Mounjaro (tirzepatide). This happens because Mounjaro slows how quickly food moves through your stomach, which can change how your digestive system processes food and gas. The effect is usually temporary and most commonly occurs during the initial dose titration phase. Understanding why this happens and how to manage it can help you decide whether Mounjaro is right for you. Use our free GLP-1 weight loss calculator to explore potential outcomes if you're considering this medication.
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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 Mounjaro Causes Sulphur Burps and Digestive Changes
Mounjaro works as a dual GIP and GLP-1 receptor agonist, activating two natural hormone pathways that regulate appetite and digestion. One key effect is that it slows gastric emptying — the speed at which food leaves your stomach and enters your small intestine. When food stays in your stomach longer, it undergoes prolonged fermentation and bacterial breakdown, which produces hydrogen sulphide gas. This gas creates the distinctive rotten egg or sulphur smell when you burp.
The sulphide compounds are produced naturally during digestion, but normally pass through your system quickly. With Mounjaro slowing this process, especially during the dose titration phase when your body is adjusting, you may notice these burps more frequently. This side effect is not dangerous — it is simply an uncomfortable digestive phenomenon. Most people find that sulphur burps reduce or disappear as their body adapts to the medication, typically after 4–8 weeks on a stable dose.
- Occurs more often in the first 4 weeks of starting Mounjaro or increasing your dose
- Related to slower stomach emptying, not a sign of infection or serious illness
- More noticeable after eating fatty or protein-heavy meals
- Usually settles within weeks as your digestive system adapts
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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 Accessing Mounjaro in the UK
If you experience sulphur burps on Mounjaro, several practical strategies may help: eat smaller, more frequent meals; avoid fatty or heavily processed foods; stay hydrated; take regular walks after eating; and eat slowly. In the UK, Mounjaro is available through two routes. NHS access is through specialist tier 3 weight management services following GP referral, though waiting lists vary significantly by region and ICB availability. Private access is through a UK-licensed prescriber following an online clinical assessment — you can access treatment without NHS referral, and your prescriber will assess eligibility based on your BMI and health status. Pricing for private prescriptions varies, but Mounjaro typically ranges from £129 to £320+ monthly depending on your dose. Your prescriber will discuss expected side effects, including sulphur burps, before you begin treatment.
- Smaller meals and slower eating can reduce gas production
- Avoiding high-fat foods temporarily may ease symptoms
- Both NHS and private routes are available in the UK
- Discuss all potential side effects with your prescriber before starting
- 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 serious side effect of Mounjaro?
No. Sulphur burps are uncomfortable but not dangerous. They are caused by slower stomach emptying and natural digestive processes, not infection or illness. They typically resolve within a few weeks as your body adapts to the medication. If burps persist beyond 8 weeks or are accompanied by severe abdominal pain, contact your GP.
How long do sulphur burps last when taking Mounjaro?
Most people find sulphur burps reduce or disappear within 4–8 weeks once their body adjusts to the medication. They are usually most noticeable during the initial dose titration phase. If they persist longer, your prescriber may adjust your dose or recommend dietary changes.
Can I reduce sulphur burps by changing what I eat?
Yes. Eating smaller portions, avoiding fatty or fried foods, staying hydrated, and eating slowly can all help reduce gas production and sulphur burps. Some people also find that taking a short walk after meals improves digestion and reduces symptoms.
Is Mounjaro available on the NHS in the UK?
Yes, Mounjaro (tirzepatide) is available through NHS specialist weight management services for eligible adults. Access requires referral from your GP to a tier 3 service. Availability and waiting times vary by region. Private prescriptions are also available through UK-licensed prescribers following an online clinical assessment.
What other digestive side effects does Mounjaro cause?
Common digestive side effects include nausea, diarrhoea, constipation, vomiting, and stomach pain — most are mild and temporary. Sulphur burps are less common than these but still reported by some users. Your prescriber will discuss all potential side effects before you start treatment.
Ready to take control of your weight loss journey?
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