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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Mounjaro and Sulfur Burps — What You Need to Know
Sulfur burps (rotten egg-smelling belches) are a recognised gastrointestinal side effect some people experience when taking Mounjaro (tirzepatide) for weight management. While not everyone experiences this symptom, it's one of several digestive effects associated with GLP-1 and dual GIP/GLP-1 receptor agonist medications in the UK. Understanding what causes it and how to manage it can help you stay comfortable while using this prescription-only weight loss injection.
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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.
What Causes Sulfur Burps on Mounjaro?
Sulfur burps on Mounjaro occur due to how the medication affects your digestive system. Tirzepatide slows gastric emptying — the rate at which food moves from your stomach into your small intestine. This slower digestion allows food to sit in the stomach longer, creating an environment where bacteria produce hydrogen sulphide gas, which creates the characteristic rotten egg smell.
This effect typically occurs alongside other common GI side effects listed in Mounjaro's UK guidance:
- Nausea and indigestion
- Diarrhoea or constipation
- Stomach (abdominal) pain
- Acid reflux (GORD)
Sulfur burps are usually mild and temporary, often improving as your body adjusts to the medication over several weeks. However, the symptom may also ease as your prescriber gradually increases your Mounjaro dose during the titration phase — moving from 2.5 mg through to 5 mg, 7.5 mg, and higher as needed over weeks 1–20.
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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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How to Manage Sulfur Burps — Practical Tips
While sulfur burps typically reduce over time, several evidence-based strategies may help reduce severity:
- Eat smaller, more frequent meals — reduces the amount of food in your stomach at once, limiting fermentation
- Eat slowly and chew thoroughly — aids digestion and reduces gastric stress
- Avoid trigger foods — fatty, greasy, or high-protein foods may worsen symptoms; track what increases burps using our free progress tracker
- Stay hydrated — drinking water throughout the day supports digestive function
- Light activity after eating — a short walk can aid gastric emptying
- Speak to your GP — if sulfur burps persist beyond 4–6 weeks or significantly impact your quality of life, your prescriber may adjust your dose or offer alternative management
Remember that Mounjaro side effects vary widely — some people experience no sulfur burps at all, whilst others find it more pronounced.
- 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 sulfur burps a sign that Mounjaro isn't working?
No. Sulfur burps are a gastrointestinal side effect unrelated to Mounjaro's weight loss effectiveness. Many people who experience sulfur burps still lose weight successfully on the medication. The symptom typically improves as your body adjusts, usually within 2–6 weeks.
Should I stop taking Mounjaro if I get sulfur burps?
No — you should not stop without speaking to your prescriber first. Sulfur burps are usually temporary and manageable. If the symptom is severe or doesn't improve after several weeks, contact your GP or prescriber to discuss dose adjustment or other options rather than stopping suddenly.
Can I prevent sulfur burps before they start?
There's no assured way to prevent them, as they depend on individual digestive response. However, starting with smaller meals and avoiding fatty foods from the beginning may reduce the likelihood or severity. Your prescriber will start you on the lowest dose (2.5 mg) during week 1–4, which may minimise early symptoms.
Is sulfur burps a reason not to take Mounjaro in the UK?
No. Sulfur burps affect only some people and are typically mild and temporary. The NHS considers Mounjaro appropriate for eligible adults because the weight loss benefits and improvement in weight-related health conditions often outweigh temporary digestive side effects. Your GP can discuss whether it's suitable for you.
How does sulfur burps on Mounjaro compare to other GLP-1 medications like Wegovy?
Sulfur burps can occur with any GLP-1 or GIP/GLP-1 medication because they all slow gastric emptying. Wegovy (semaglutide) users report similar symptoms. Individual experience varies greatly — some people tolerate one medication better than another. Your prescriber can help assess which option suits you if you experience problematic side effects.
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