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 You Get Sulphur Burps on Mounjaro?
Sulphur burps (also called rotten egg burps) are a reported side effect of Mounjaro in some people. These unpleasant burps happen because tirzepatide slows how quickly food moves through your digestive system, allowing bacteria in your gut to ferment food for longer. This fermentation produces hydrogen sulphide gas, which creates that distinctive sulphur smell. While not everyone experiences this, understanding why it happens can help you manage it effectively. This guide explains the mechanism, how common it is, and practical steps to reduce or prevent sulphur burps while using Mounjaro.
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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 Causes Sulphur Burps
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — a prescription-only weight management injection licensed in the UK. One of its mechanisms of action is slowing gastric emptying, which means food stays in your stomach and digestive tract longer than usual. This delayed digestion can create an environment where gut bacteria ferment food, producing hydrogen sulphide gas as a byproduct. The result is burps with a distinctive rotten egg or sulphur smell.
This side effect typically occurs because:
- Food moves more slowly through your digestive system
- Bacteria in your gut have more time to ferment undigested food
- Hydrogen sulphide gas is produced during bacterial fermentation
- This gas is released as burps rather than passing through your bowels
The good news is that this effect often reduces over time as your body adjusts to the medication. However, it can be managed with dietary and lifestyle changes in the meantime.
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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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How Common Are Sulphur Burps on Mounjaro?
Sulphur burps are not listed as a "very common" side effect in the official product information, but they are frequently reported by Mounjaro users in the UK and internationally. They appear to be more common in the first 4–12 weeks of treatment, particularly during the dose escalation phase when your body is adjusting to the medication's effects on your digestive system.
Individual experiences vary widely — some people never experience them, whilst others find them bothersome. If you're considering Mounjaro or currently taking it, a GLP-1 weight loss calculator can help you understand projected outcomes, and your prescriber can discuss specific side effects during your clinical assessment.
- 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.
What causes sulphur burps on Mounjaro specifically?
Mounjaro slows how quickly food leaves your stomach (gastric emptying). This delayed digestion allows gut bacteria to ferment food longer, producing hydrogen sulphide gas. This gas is released as burps with a rotten egg or sulphur smell. The effect typically reduces as your body adjusts to the medication.
Are sulphur burps a sign that Mounjaro isn't working?
No. Sulphur burps are a side effect related to how Mounjaro works (slowed digestion), not a sign of effectiveness or ineffectiveness. Many people who experience sulphur burps continue to lose weight successfully. This is separate from the medication's weight management action.
How long do sulphur burps last on Mounjaro?
Sulphur burps are often worst during the first 4–12 weeks, particularly during dose escalation. Most people find they improve significantly after 8–16 weeks as the body adjusts. Some people experience them intermittently throughout treatment; others stop entirely. Duration varies individually.
Can you prevent sulphur burps when taking Mounjaro?
Whilst you can't eliminate them entirely, you can reduce them by eating slowly, chewing thoroughly, avoiding high-fat and high-sulphur foods, staying hydrated, and eating smaller, more frequent meals. Ginger tea, peppermint tea, and probiotic foods may also help. Speak to your GP if they're severe.
Should you stop Mounjaro if you get sulphur burps?
Sulphur burps alone are not a reason to stop Mounjaro — they're a temporary side effect that usually improves with time and dietary adjustment. However, if they're severely impacting your quality of life, discuss this with your prescriber. They may adjust your dose or offer additional management strategies.
Ready to take control of your weight loss journey?
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