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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Eggy Burps on Mounjaro — How It Compares to Wegovy
Eggy burps (sulphur-like belching) are a reported side effect that some people experience when taking Mounjaro for weight management. This guide compares how Mounjaro and Wegovy differ in their mechanisms, trial data, and reported side effects — including gastrointestinal symptoms. Both are prescription-only GLP-1-related medications licensed in the UK, but they work differently. Understanding these differences can help you discuss which medication might suit you best with your GP or prescriber. Individual experiences vary significantly between users.
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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.
Mechanism Differences — GLP-1 Only vs Dual Action
Wegovy (semaglutide) is a GLP-1 receptor agonist — it activates one hormone pathway to reduce appetite and slow gastric emptying. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, activating two hormone pathways simultaneously. This dual mechanism may affect how your digestive system responds, which could influence side effects like eggy burps. In STEP trials, Wegovy users reported nausea and gastrointestinal discomfort as common side effects. In SURMOUNT trials, Mounjaro users similarly reported nausea, diarrhoea, and stomach discomfort. Both medications slow how food moves through your stomach, which can cause gas, bloating, and sulphur-like belching in some people. The dual mechanism of Mounjaro doesn't necessarily mean more or fewer gastrointestinal issues — it varies between individuals. Clinical trial data shows both medications have similar rates of common digestive side effects, though individual tolerance differs significantly.
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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.
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Weight Loss Results and Individual Suitability
Clinical trials showed Wegovy achieved average weight loss of approximately 15% body weight (STEP-1, 68 weeks). Mounjaro achieved average weight loss of 15–21% body weight depending on dose (SURMOUNT-1, 72 weeks). However, average results don't predict individual outcomes. Some people experience minimal side effects; others find gastrointestinal symptoms limiting. Side effect tolerance — including eggy burps — often improves as your body adjusts over weeks, though this isn't assured. Your prescriber will assess which medication is suitable based on your individual health, medical history, and tolerance. Both require a clinical assessment before prescription. Use our free GLP-1 weight loss calculator to explore projected outcomes, and our BMI calculator to understand your current health context. Neither medication is "better" — suitability is individual.
- 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.
Why do some people get eggy burps on Mounjaro?
Eggy burps (sulphur-like belching) occur because GLP-1 medications slow gastric emptying and alter gut bacteria activity. Gas production increases temporarily, and as your digestive system adjusts, some of this gas is released as burps with a distinctive smell. This typically improves after several weeks as your body adapts to the medication.
Do Mounjaro and Wegovy cause eggy burps at the same rate?
Both medications report similar rates of gastrointestinal side effects in clinical trials, including nausea and stomach discomfort. Eggy burps aren't specifically measured in trials, so direct comparison data is limited. Individual experience varies — some people on either medication experience them; others don't. Your experience depends on your body's response and dose.
Can you reduce eggy burps while taking Mounjaro?
Yes. Eat smaller, more frequent meals; avoid high-fat and high-fibre foods initially; stay hydrated; and take gentle exercise to aid digestion. Most people find symptoms improve naturally within 4–12 weeks as their body adjusts. If eggy burps persist severely, discuss with your prescriber — they may adjust your dose or suggest alternative management strategies.
Is Mounjaro's dual mechanism more likely to cause eggy burps than Wegovy?
Not necessarily. Both medications cause similar rates of gastrointestinal side effects. Mounjaro's dual GIP and GLP-1 action may affect some people differently, but clinical data doesn't show it causes more digestive issues overall. Individual tolerance varies more than medication type. Your prescriber will advise based on your personal health profile.
Should I choose between Mounjaro and Wegovy based on eggy burps?
Side effect tolerance is one factor, but not the only consideration. Your prescriber will assess your BMI, medical history, other medications, and eligibility based on NHS criteria before recommending either. If you experience concerning side effects on one medication, your prescriber may adjust the dose or suggest an alternative. Both require a clinical assessment — discuss your concerns openly with your GP.
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