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 Benefits in the UK — How It Compares to Wegovy
Mounjaro (tirzepatide) and Wegovy (semaglutide) are both prescription weight loss injections licensed in the UK, but they work differently and deliver different clinical outcomes. Understanding how they compare helps you and your prescriber make an informed decision about which medication might suit your individual needs. This guide breaks down the evidence from clinical trials, how each works, and what "benefits" really means in practice.
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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.
Clinical Trial Results — SURMOUNT vs STEP Data
The strongest difference between Mounjaro and Wegovy lies in their clinical trial results. Mounjaro (SURMOUNT-1 trial) showed average weight losses of approximately 15% at 5 mg, 19.5% at 10 mg, and 20.9% at the maximum 15 mg dose over 72 weeks. Wegovy (STEP-1 trial) showed average weight loss of approximately 14.9% at the maximum 2.4 mg dose over 68 weeks.
Both trials included participants following a reduced-calorie diet and increased physical activity. Individual results vary significantly — some people lose more, some less. The difference between the two medications is modest; many people respond equally well to either. Trial participants also had different baseline characteristics, so direct comparison requires caution. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses.
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How It Works
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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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Mechanism of Action — Why They're Different
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist. It activates two natural hormone pathways: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). This dual mechanism may explain why some people experience greater appetite reduction with Mounjaro.
Wegovy (semaglutide) is a GLP-1 receptor agonist only. It activates the GLP-1 pathway alone. Both mechanisms reduce appetite and support feeling fuller after eating, but the dual action of Mounjaro may offer an additional benefit for some individuals. Neither medication is "better" — response is personal. Your prescriber will assess which suits your health profile.
- 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.
Does Mounjaro cause more weight loss than Wegovy?
Clinical trials show Mounjaro resulted in slightly higher average weight loss (up to 20.9%) compared to Wegovy (14.9%), but individual results vary greatly. Some people respond equally well to Wegovy; others prefer Mounjaro. Your prescriber will recommend based on your medical history, not trial averages.
What is the main difference between how Mounjaro and Wegovy work?
Mounjaro is a dual GIP+GLP-1 receptor agonist (activates two hormone pathways), while Wegovy is a GLP-1-only agonist. The dual mechanism in Mounjaro may enhance appetite suppression for some people, but both medications reduce hunger and support sustainable weight loss.
Can I switch from Wegovy to Mounjaro if I'm not seeing results?
Yes, switching between medications is possible and is managed by your prescriber. A rough equivalence exists (Wegovy 2.4 mg ≈ Mounjaro 15 mg), but any switch requires clinical assessment. Never change medications without consulting your GP or prescriber.
Which weight loss injection is available on the NHS in the UK?
Both Mounjaro and Wegovy are approved for NHS use through specialist tier 3 weight management services. Availability varies significantly by region and NHS waiting lists can be lengthy. Private prescription is also available through licensed UK prescribers.
How do I know which medication is right for me — Mounjaro or Wegovy?
Your GP or licensed prescriber will assess your medical history, current medications, BMI, and any weight-related health conditions. Neither medication is universally "better"; suitability is individual. Use our free BMI calculator to understand your starting point, then discuss options with your healthcare provider. ```
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