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 I Get Sulphur Burps On Mounjaro?
Sulphur burps (rotten egg-smelling belches) are a known side effect that some people experience when taking Mounjaro (tirzepatide). This happens because the medication slows how quickly food moves through your stomach, allowing gases to build up and create that distinctive smell. While unpleasant, sulphur burps typically improve as your body adjusts to the medication. Understanding why this happens and what you can do about it may help you manage this side effect more effectively during your treatment.
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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 key mechanisms is slowing gastric emptying, which means food stays in your stomach longer. This delayed digestion can cause bacterial fermentation of food in your digestive tract, producing hydrogen sulphide gas — the compound responsible for that rotten egg smell.
When this gas builds up in your stomach and is released as a burp, you experience the characteristic sulphur burp sensation. This is more likely to occur when you eat fatty, greasy, or protein-rich foods, as these take longer to digest. The effect typically decreases over time as your body adjusts to the medication and your dose stabilises during the dose titration phase.
- Delayed stomach emptying is an intentional effect of Mounjaro — it helps you feel fuller longer
- Bacterial fermentation in a slower-moving digestive system creates hydrogen sulphide
- Individual experiences vary significantly — not everyone on Mounjaro experiences sulphur burps
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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
Several practical strategies may help reduce sulphur burps whilst taking Mounjaro. Eat smaller, more frequent meals rather than large portions, as this reduces the volume of food fermenting in your stomach at once. Avoid fatty, fried, and heavily processed foods — stick to lean proteins, vegetables, and whole grains that digest more easily. Stay hydrated throughout the day and avoid carbonated drinks, which can increase gas buildup.
Eating slowly and chewing food thoroughly also helps. Some people find that taking a short walk after eating improves digestion and reduces gas accumulation. If sulphur burps persist beyond the first few weeks of treatment or become distressing, speak to your prescriber or GP — they may adjust your dose or suggest additional strategies tailored to your individual needs.
- 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.
How long do sulphur burps last on Mounjaro?
Sulphur burps typically improve within the first 2–4 weeks as your body adapts to the medication and dose titration progresses. For most people, they become much less frequent or disappear entirely by 8–12 weeks. However, individual experiences vary — some people never experience them, whilst others find them persistent. Keep a diary to track patterns and discuss ongoing symptoms with your GP or prescriber.
Are sulphur burps a sign Mounjaro isn't working?
No. Sulphur burps are a side effect of how Mounjaro works (slowing stomach emptying), not an indicator of treatment success or failure. Weight loss results from the medication's dual GIP and GLP-1 action on appetite and food intake — separate from digestive side effects. Use our free GLP-1 weight loss calculator to track projected results alongside your symptom management.
Can I prevent sulphur burps on Mounjaro?
Complete prevention isn't assured, but you can reduce frequency significantly by eating smaller meals, avoiding fatty foods, staying hydrated, and eating slowly. Carbonated drinks, artificial sweeteners, and high-fat proteins tend to trigger them more often. Experiment with different foods to identify your personal triggers and adjust your diet accordingly during dose titration.
Should I stop taking Mounjaro if I get sulphur burps?
No — sulphur burps alone are not a reason to stop treatment. They're a temporary side effect that improves over time for most people. However, if sulphur burps are severe or combined with other concerning symptoms (persistent nausea, vomiting, abdominal pain), contact your GP or prescriber immediately. They can assess whether the dose needs adjusting or whether alternative support is needed.
Are sulphur burps more common with higher Mounjaro doses?
Side effects including digestive symptoms like sulphur burps may be more noticeable at higher doses, but individual variation is significant. During dose titration — where you start at 2.5 mg and increase weekly — your body has time to adapt. Some people experience sulphur burps at lower doses and none at higher doses, whilst others follow the opposite pattern. Your prescriber can help monitor this.
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