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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Is Mounjaro Approved For Weight Loss in the UK?
Yes, Mounjaro (tirzepatide) is fully approved in the UK for weight management in adults. It's a prescription-only, once-weekly injectable medicine that activates two natural hormone pathways — GIP and GLP-1 — making it structurally different from other weight loss injections like Wegovy. Both medications are licensed for weight loss, but they work through different mechanisms and have different clinical trial profiles. Your prescriber will assess which might be more suitable for your individual circumstances following a clinical assessment.
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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.
How Do Mounjaro and Wegovy Compare in UK Trials?
Mounjaro (SURMOUNT trial data): In the SURMOUNT-1 clinical trial, participants taking Mounjaro 15 mg (the maximum dose) lost an average of approximately 20.9% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity. At the 10 mg dose, average weight loss was around 19.5%.
Wegovy (STEP trial data): In the STEP-1 trial, participants on Wegovy 2.4 mg (maximum dose) lost approximately 14.9% of body weight over 68 weeks under similar lifestyle conditions.
These are clinical trial averages — individual results vary significantly. The key difference is mechanism: Mounjaro is a dual GIP and GLP-1 receptor agonist, whilst Wegovy is a GLP-1-only agonist. This dual action may explain the slightly higher average weight loss seen with Mounjaro in trials, though prescriber choice depends on many factors beyond trial data alone.
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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.
How Do Prescribers Decide Between Them?
Both Mounjaro and Wegovy are prescription-only medicines requiring clinical assessment by a UK-licensed prescriber. Your eligibility, medical history, other medications, and any contraindications will all inform the decision. Try our free GLP-1 weight loss calculator to explore potential outcomes at different doses — this can be a useful discussion point with your prescriber.
Access in the UK is through NHS specialist weight management services (where availability varies significantly by region) or private online prescribing following an assessment. Doses are escalated gradually over weeks — Mounjaro ranges from 2.5 mg to 15 mg weekly, whilst Wegovy ranges from 0.25 mg to 2.4 mg weekly. Neither medication assures weight loss; results depend on adherence, lifestyle changes, and individual metabolism.
- 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.
Is Mounjaro approved by the MHRA for weight loss?
Yes. Mounjaro (tirzepatide) is fully approved by the MHRA for weight management in UK adults. It received approval for this indication and is subject to additional monitoring (Black Triangle status). It's available as a prescription-only, once-weekly injectable via both NHS specialist services and private prescribing.
What is the main difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 receptor agonist, whilst Wegovy is a GLP-1-only agonist. This dual mechanism in Mounjaro may contribute to slightly higher average weight loss in clinical trials, though individual outcomes vary. Both are once-weekly injections but have different dose ranges and escalation schedules.
Which weight loss injection is better — Mounjaro or Wegovy?
Neither is universally "better" — suitability is individual. Your prescriber will assess your medical history, other medications, and health goals. Clinical trial data shows Mounjaro achieved higher average weight loss, but both are effective. Use our free GLP-1 calculator to explore potential outcomes and discuss options with your healthcare provider.
Can I get Mounjaro on the NHS for weight loss?
Mounjaro is available through NHS specialist weight management services (tier 3/4) in some regions, following referral from your GP. Availability varies significantly by area and waiting lists can be long. Private access is available via a UK-licensed prescriber following an online assessment. Your GP can advise on NHS options in your area.
How is Mounjaro prescribed — what dose do I start on?
Mounjaro uses a gradual dose titration schedule. You start at 2.5 mg weekly for weeks 1–4, then increase every 4 weeks (5 mg, 7.5 mg, 10 mg, 12.5 mg, 15 mg maximum). This approach helps minimise side effects. Your prescriber will decide the escalation pace based on your tolerance and response. Check your weight with our free BMI calculator to track progress.
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.