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 UK Patients Need to Know
Sulphur burps (also called rotten egg burps) are a recognised side effect reported by some people taking Mounjaro (tirzepatide) in the UK. This happens because Mounjaro slows how quickly food moves through your stomach, which can change how your gut bacteria break down food. While uncomfortable, sulphur burps are usually temporary and tend to improve as your body adjusts to the medication. Understanding what causes them and when to seek help from your GP is important for managing your Mounjaro prescription effectively.
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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 Mounjaro Causes Sulphur Burps in UK Patients
Sulphur burps occur due to delayed gastric emptying — a known effect of GLP-1 and GIP receptor agonists like Mounjaro (tirzepatide). When food stays in your stomach longer than usual, it undergoes prolonged fermentation by gut bacteria. This process produces hydrogen sulphide gas, which escapes as burps with a distinctive rotten egg smell.
This side effect is temporary in most cases. As your body adjusts to the medication over weeks, your digestive system adapts and sulphur burps typically reduce or resolve completely. The effect is most noticeable during the first 4–8 weeks and during dose increases.
Other related gastrointestinal effects you may experience include nausea, bloating, indigestion, or changes in bowel habits. These are all listed as common side effects in the Mounjaro patient information leaflet. If sulphur burps persist beyond 8 weeks or become severe, contact your GP or the prescriber who issued your Mounjaro prescription.
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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 Sulphur Burps While on Mounjaro
Practical steps to reduce sulphur burps:
- Eat smaller, more frequent meals rather than large meals — this reduces fermentation time
- Chew food thoroughly to aid digestion
- Stay well hydrated and drink water throughout the day
- Avoid foods that increase gas production: beans, cruciferous vegetables, carbonated drinks, and high-fat foods
- Take a gentle walk after meals to encourage normal digestion
- Consider taking an over-the-counter probiotic to support healthy gut bacteria balance
If you experience severe bloating, persistent vomiting, or abdominal pain alongside sulphur burps, contact your GP immediately. These could indicate a more serious digestive issue. Your prescriber may suggest adjusting your Mounjaro dose or temporarily pausing treatment whilst investigating.
- 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 that Mounjaro isn't right for me?
No. Sulphur burps are a temporary side effect that resolves for most people as their body adapts to Mounjaro. They're listed as a common side effect and do not mean the medication is unsuitable. Discuss any persistent concerns with your GP or prescriber, who can advise on managing symptoms or dose adjustments.
How long do sulphur burps last when taking Mounjaro?
Sulphur burps typically appear within the first 2–4 weeks of starting Mounjaro or increasing your dose. For most people, they improve significantly by week 6–8 as your digestive system adjusts. Some people experience them only during dose escalations. If they persist beyond 8 weeks, contact your prescriber for guidance.
Can I use the GLP-1 weight loss calculator to predict how long side effects will last?
Our weight loss calculator helps estimate potential weight loss outcomes with Mounjaro at different doses, but it doesn't predict individual side effect timelines. Side effects vary between people based on individual metabolism and digestive factors. Your prescriber can give personalised guidance based on your health history.
Should I stop taking Mounjaro if I get sulphur burps?
Do not stop taking Mounjaro without speaking to your prescriber first. Sulphur burps are usually temporary and manageable. If they're severe or combined with vomiting, severe nausea, or abdominal pain, contact your GP immediately. Your prescriber may suggest dietary adjustments, a temporary dose pause, or other management strategies before considering stopping.
Is there a difference between sulphur burps on Mounjaro versus Wegovy?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) slow gastric emptying, so sulphur burps can occur with either medication. Mounjaro's dual GIP and GLP-1 mechanism may affect digestion slightly differently than Wegovy's single GLP-1 mechanism, but individual experiences vary widely. Your prescriber can discuss which medication may be better tolerated for your specific situation.
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