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 Does Mounjaro Cause Sulphur Burps?
Sulphur burps (also called rotten egg burps) are a reported side effect of Mounjaro (tirzepatide), the prescription-only weight management injection. This uncomfortable symptom occurs because of how Mounjaro affects your digestion, particularly by slowing how quickly food moves through your stomach. Whilst not everyone experiences sulphur burps on Mounjaro, they're common enough that it's worth understanding why they happen and what you can do about them.
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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 Affects Your Digestion
Mounjaro is a dual GIP and GLP-1 receptor agonist — this means it activates two natural hormone pathways that help regulate appetite and blood sugar. One key way it works is by slowing gastric emptying, the rate at which food leaves your stomach and enters your small intestine. This slower digestion is actually part of how the medication helps you feel fuller for longer.
When food stays in your stomach longer than usual, bacteria in your gut have more time to break it down. This bacterial fermentation process produces hydrogen sulphide gas — the compound responsible for that distinctive rotten egg or sulphur smell. The gas then escapes as burps, which is why you experience sulphur-smelling breath.
- Slower stomach emptying = longer food digestion time
- Extended digestion allows more bacterial fermentation
- Hydrogen sulphide gas is produced as a natural byproduct
- This effect is particularly common in the early weeks of Mounjaro therapy
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If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
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Managing Sulphur Burps on Mounjaro
Sulphur burps are usually temporary and tend to improve as your body adjusts to Mounjaro — typically within the first few weeks as your digestive system adapts. However, several practical strategies may help reduce their frequency and severity.
- Eat smaller, more frequent meals — reduces the amount of food fermenting at once
- Choose easily digestible foods — lean proteins, vegetables, and wholegrain carbohydrates
- Avoid sulphur-rich foods — eggs, cruciferous vegetables (broccoli, cabbage), onions, and garlic temporarily
- Stay hydrated — drinking water supports healthy digestion
- Ginger or peppermint tea — may help with digestion and gas
If sulphur burps persist beyond a few weeks or significantly affect your quality of life, discuss this with your prescriber — dose adjustment may help.
- 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?
Most people find sulphur burps improve within 2–4 weeks as their body adjusts to the medication. However, individual timelines vary. If they persist beyond 4 weeks or worsen, contact your prescriber. They may adjust your dose titration schedule or suggest dietary modifications to help manage the symptom.
Are sulphur burps a sign that Mounjaro isn't working?
No. Sulphur burps are a side effect of how Mounjaro affects digestion — not a sign of effectiveness or failure. Many people experience sulphur burps but still achieve good weight loss results. The medication's weight management benefits are separate from this temporary digestive side effect.
Can I prevent sulphur burps before they start?
You can't always prevent them, but certain dietary choices may reduce their likelihood. Eating smaller meals, choosing easily digestible foods, and avoiding sulphur-rich foods like eggs and cruciferous vegetables during the first few weeks may help. Starting with the lowest Mounjaro dose (2.5 mg) also minimises early digestive side effects.
Should I stop taking Mounjaro if I get sulphur burps?
No — sulphur burps are temporary and typically resolve on their own. This is a common, manageable side effect, not a reason to discontinue treatment. However, always discuss any persistent or bothersome side effects with your prescriber. They can provide personalised advice and may suggest dose adjustments or strategies to help.
Are sulphur burps worse on higher Mounjaro doses?
Digestive side effects, including sulphur burps, can vary with dose. Some people find symptoms improve after the first few weeks on each dose, whilst others notice more digestive effects at higher doses like 10 mg or 15 mg. Your prescriber manages dose titration carefully, typically increasing every 4 weeks, to allow your body to adapt.
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