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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What Are Sulphur Burps on Mounjaro?
Sulphur burps (also called rotten egg burps) are a known side effect of Mounjaro that some users experience. These occur because tirzepatide slows how quickly food moves through your stomach, allowing bacteria to ferment food and produce sulphur-smelling gas. While uncomfortable, sulphur burps are not dangerous and typically reduce as your body adjusts to the medication. Understanding what causes them and how they differ from other GLP-1 side effects can help you manage this common Mounjaro side effect 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
Sulphur burps happen because tirzepatide (the active ingredient in Mounjaro) slows gastric emptying — the rate at which food leaves your stomach. When food stays in your stomach longer, bacteria naturally present in your digestive system ferment the food, producing hydrogen sulphide gas that creates that characteristic rotten egg smell.
This mechanism is different from Wegovy (semaglutide), which also slows gastric emptying but appears to cause sulphur burps less frequently in clinical practice. Both medications are GLP-1 receptor agonists, but Mounjaro is a dual GIP and GLP-1 agonist — it activates two hormone pathways rather than one. This dual action may explain why some users report sulphur burps more commonly on Mounjaro than on Wegovy, though individual experiences vary significantly.
The effect typically lessens as your body adapts over weeks 4–8 of treatment. Gastric emptying gradually returns to normal despite continuing the medication, so sulphur burps often resolve or become much less noticeable even whilst staying on your dose.
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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 Help
Several practical steps can reduce sulphur burps: eat smaller, more frequent meals; avoid high-fat and high-fibre foods (which ferment more easily); chew food thoroughly; stay hydrated; and consider ginger tea or peppermint, which may aid digestion. Keeping a food diary using our free progress tracker can help you identify which foods trigger them most.
If sulphur burps are severe or persist beyond 8 weeks, contact your prescriber — they may adjust your Mounjaro dose or suggest alternative timing for meals. Sulphur burps alone are not a reason to stop Mounjaro, but your prescriber needs to know if they're affecting your quality of life. Always discuss any persistent or concerning side effects with your GP or the prescriber who initiated your treatment.
- 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 dangerous on Mounjaro?
No, sulphur burps are not dangerous. They are an uncomfortable but harmless side effect caused by slower stomach emptying. They do not indicate a serious problem and typically improve as your body adjusts to the medication over the first 4–8 weeks.
Do sulphur burps happen on Wegovy too?
Sulphur burps can occur on Wegovy (semaglutide), but they are reported less frequently than on Mounjaro. Both slow gastric emptying, but Mounjaro's dual GIP+GLP-1 mechanism may make them slightly more common. Individual experiences vary considerably.
How long do sulphur burps last on Mounjaro?
Most users report sulphur burps improve or disappear within 4–8 weeks as the body adjusts. However, some people experience them longer or intermittently. Dietary adjustments can help reduce their frequency and intensity during this adjustment period.
What foods make sulphur burps worse on Mounjaro?
High-fat, high-fibre, and difficult-to-digest foods typically worsen sulphur burps because they ferment more easily in a slower-moving stomach. Fried foods, cruciferous vegetables, and beans are common triggers. Keeping a food diary can help identify your personal triggers.
Should I stop Mounjaro if I get sulphur burps?
Sulphur burps alone are not a reason to stop Mounjaro. However, if they significantly impact your quality of life or persist beyond 8 weeks despite dietary changes, discuss this with your prescriber. They can advise whether to continue, adjust your dose, or explore alternatives.
Ready to take control of your weight loss journey?
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