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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Egg Burps on Mounjaro vs Wegovy — What's the Difference?
Egg burps (sulphur-smelling burps) are a recognised side effect reported by some people taking Mounjaro and Wegovy. Both medications can slow gastric emptying, which may contribute to this symptom. This guide compares how Mounjaro (tirzepatide) and Wegovy (semaglutide) work, what clinical trials showed, and how individual suitability is determined. Use our free GLP-1 weight loss calculator to explore potential outcomes with either medication, and remember that individual experiences vary significantly. Always consult your GP for personalised advice.
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Calculate Your BMI Instantly
Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
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 and Wegovy Differ — Mechanism and Trial Outcomes
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways to regulate appetite and support feeling fuller after meals. Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single pathway.
In the SURMOUNT-1 clinical trial, participants on Mounjaro 15 mg lost an average of 20.9% of their body weight over 72 weeks alongside a reduced-calorie diet and physical activity. In the STEP-1 trial, Wegovy participants on 2.4 mg lost approximately 14.9% of body weight over 68 weeks under the same conditions.
Both medications may cause gastrointestinal side effects including nausea, diarrhoea, constipation, and stomach discomfort. Egg burps appear in post-marketing reports for both but are not formally listed as common side effects in the UK product information. The dual mechanism of Mounjaro may theoretically affect gastric function differently than Wegovy's single mechanism, though individual variation is substantial.
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How It Works
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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Suitability and Prescribing — Your GP Will Assess You
Both Mounjaro and Wegovy are prescription-only medicines in the UK requiring a clinical assessment before prescribing. Eligibility criteria are the same: a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease.
If you experience troublesome egg burps or other side effects, your prescriber may adjust your dose, switch you to the other medication, or recommend supportive strategies such as dietary modifications and peppermint tea. There is no established official conversion between Mounjaro and Wegovy doses—any switch must be managed by your prescriber.
Track your progress and side effect patterns using our free progress tracker to share detailed information with your GP. Your individual medical history, tolerability, and response will guide which medication is most suitable for you.
- 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.
What causes egg burps on Mounjaro and Wegovy?
Both medications slow how quickly food leaves your stomach (gastric emptying). This can lead to increased fermentation of food in the digestive tract, producing hydrogen sulphide gas and creating the distinctive sulphur smell. The effect may reduce as your body adjusts over weeks or months.
Are egg burps more common on Mounjaro or Wegovy?
Post-marketing reports suggest both medications can cause egg burps, but there is no large-scale comparative data on frequency. Individual variation is significant—some people experience them, others do not. Mounjaro's dual mechanism may affect digestion differently, but clinical trial data does not formally compare this symptom between the two.
How long do egg burps last on these medications?
Egg burps typically improve as your body adjusts to the medication, often within weeks to a few months. If they persist or become severe, discuss with your prescriber about dose adjustment, dietary changes, or whether a different medication might be better tolerated. Peppermint tea and ginger may help some people.
Should I stop taking Mounjaro or Wegovy because of egg burps?
Do not stop without speaking to your prescriber first. Egg burps are temporary for most people and manageable. Your prescriber can help you decide whether to continue, adjust the dose, switch medications, or try supportive measures. The benefits of the medication may outweigh this side effect for you personally.
Can I use the BMI calculator to check if I'm eligible for either medication?
Yes—use our free BMI calculator to see where your weight falls on the NHS scale. However, BMI is only one part of eligibility. Your GP will consider your overall health, weight-related conditions, and medical history to determine whether Mounjaro, Wegovy, or another approach is appropriate for you.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.