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 Burping and Eggs — How It Compares to Wegovy
Burping and digestive discomfort, including egg-like or rotten egg smell (sulphur burps), are reported side effects of both Mounjaro and Wegovy — though individual experiences vary significantly. Both are GLP-1-based weight loss injections available in the UK, but they work slightly differently. Understanding how these medications compare, including their side effect profiles, can help you and your prescriber decide which is more suitable for your health. This guide explains the key differences between Mounjaro (tirzepatide) and Wegovy (semaglutide), their mechanisms of action, and what burping and digestive issues mean in the context of each medication.
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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.
Mounjaro vs Wegovy — Clinical Trial Data and Mechanism
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways simultaneously. In the SURMOUNT-1 clinical trial, participants using Mounjaro at the maximum 15 mg dose lost an average of approximately 20.9% of their body weight over 72 weeks, alongside diet and exercise changes.
Wegovy (semaglutide) is a GLP-1 receptor agonist only — it activates a single pathway. In the STEP-1 clinical trial, participants using Wegovy 2.4 mg lost an average of approximately 14.9% of body weight over 68 weeks, also with lifestyle support.
- Mounjaro: dual mechanism may contribute to slightly greater average weight loss
- Wegovy: single mechanism, longer track record of use in clinical practice
- Both slow gastric emptying, which can cause burping and digestive discomfort
- Individual results vary — mechanism difference does not assures better outcomes for everyone
Use our free GLP-1 weight loss calculator to explore potential weight loss projections at different doses of either medication.
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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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Burping and Digestive Side Effects — Why They Occur
Burping and digestive issues, including sulphur-smelling burps (sometimes described as "rotten eggs"), occur because both medications slow how quickly food moves through your stomach (gastric emptying). When food spends longer in the stomach, bacterial fermentation increases, producing gas and sulphur-containing compounds — hence the unpleasant smell.
This side effect is very common with both medications during the first weeks of treatment and often improves over time as your body adjusts. It is not dangerous but can be socially uncomfortable. Eating smaller meals, avoiding fatty or overly seasoned foods, and staying hydrated may help reduce the severity. If burping persists or worsens, contact your prescriber — they may adjust your dose or suggest practical strategies. Both medications carry this risk similarly; it is not a reason to choose one over the other without considering your overall clinical picture and prescriber guidance.
- 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.
Which causes more burping — Mounjaro or Wegovy?
Both cause burping and digestive discomfort at similar rates as very common side effects. The dual mechanism of Mounjaro (GIP + GLP-1) does not specifically make burping worse. Individual tolerance varies widely — some people experience it briefly, others longer. Your prescriber can help manage it if it becomes troublesome.
What does sulphur burping mean on these medications?
Sulphur or "rotten egg" burps result from food fermenting longer in your stomach due to slowed gastric emptying. This is a normal biochemical process, not a sign of infection or serious problems. It typically reduces as your body adapts. Drinking more water and eating smaller meals may help.
How long does burping last on Mounjaro or Wegovy?
Very common digestive side effects, including burping, often peak in the first 2–4 weeks and tend to improve by weeks 8–12 as your body adjusts. Some people experience it longer. If it persists beyond 12 weeks, inform your prescriber — dose adjustment or practical strategies may help.
Can I prevent burping on these GLP-1 injections?
You cannot prevent burping entirely, but you can reduce it: eat smaller, more frequent meals; avoid greasy or highly spiced foods; stay hydrated; avoid carbonated drinks; chew food slowly and thoroughly. These strategies support digestive comfort on both Mounjaro and Wegovy.
Should I choose Wegovy over Mounjaro to avoid burping?
No — burping risk is similar between both medications. Your choice should be based on your BMI, health conditions, prescriber assessment, and suitability for the dual vs single mechanism. Burping is usually temporary. Discuss all side effects and individual factors with your prescriber to find the right medication for you.
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