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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Sulfur Burps on Mounjaro: What You Need to Know
Sulfur burps—often described as rotten egg burps—are a possible side effect of Mounjaro (tirzepatide) reported by some UK patients taking this prescription weight management injection. These unpleasant burps are caused by changes in how your digestive system processes food. Whilst not everyone experiences them, they're more common in the first few weeks of treatment. Understanding why they happen, how long they typically last, and when to contact your GP can help you manage this 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 Sulfur Burps Happen on Mounjaro
Mounjaro works by slowing gastric emptying—the rate at which food moves from your stomach into your small intestine. This delayed digestion can allow food to ferment in your stomach longer than usual, producing sulphur-containing gases that are released as burps. Additionally, Mounjaro affects gut motility and may alter your gut bacteria composition temporarily, both of which can contribute to sulphur-smelling burps.
The KwikPen injections in higher doses (10mg, 15mg) tend to cause more pronounced digestive side effects, including sulphur burps, than lower starting doses like 2.5mg or 5mg. Your body typically adjusts within 2–4 weeks as your digestive system adapts to the medication. Other common digestive changes alongside sulphur burps include nausea, constipation, and diarrhoea—all listed in the patient information for Mounjaro.
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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 Sulfur Burps and When to Seek Help
Most cases of sulphur burps resolve naturally within 2–6 weeks as your body adjusts to Mounjaro. In the meantime, eating smaller, more frequent meals; staying hydrated; and avoiding fatty or greasy foods can help reduce symptom severity. Ginger tea, peppermint, or over-the-counter digestive enzymes may provide relief, though always check with your GP before adding supplements.
Contact your prescriber or GP if sulphur burps persist beyond 6 weeks, are severely affecting your quality of life, or are accompanied by severe stomach pain—which could indicate pancreatitis. Your prescriber may adjust your dose or explore alternative options if side effects become unbearable. Use our GLP-1 weight loss calculator to review what dose might be right for you in discussion with your healthcare team.
- 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 sulfur burps last on Mounjaro?
Most patients report that sulphur burps improve within 2–4 weeks as the body adapts to tirzepatide. Some may experience them for up to 6 weeks. If they persist beyond this timeframe, contact your GP or prescriber for personalised advice.
Are sulfur burps a sign that Mounjaro isn't working?
No. Sulphur burps are a digestive side effect unrelated to whether Mounjaro is helping with weight management. They're caused by slowed stomach emptying and are temporary in most cases.
Can I prevent sulfur burps on Mounjaro?
You can reduce the risk by eating smaller meals, staying hydrated, and avoiding fatty foods from the start of treatment. Taking your injection on a day when you're eating lighter meals may also help, though side effects vary individually.
Should I stop Mounjaro if I get sulfur burps?
Sulphur burps alone are not a reason to stop treatment—they're temporary for most people. However, always discuss any bothersome side effects with your GP. Dose adjustment or timing changes might help before considering discontinuation.
Are sulfur burps more common with higher Mounjaro doses?
Yes. Starting doses like 2.5mg or 5mg cause fewer digestive issues than maintenance doses of 10mg or 15mg. Your prescriber will titrate your dose gradually to help your body adjust and minimise side effects.
Ready to take control of your weight loss journey?
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