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 Clinical Trial Results — What the NHS Data Shows
The SURMOUNT clinical trials proved Mounjaro (tirzepatide) effectiveness for weight management in UK adults. Clinical trial participants lost an average of 15–21% of their body weight over 72 weeks when using Mounjaro alongside diet and exercise. This evidence forms the basis for NHS NICE approval and current UK prescribing guidelines. Understanding the trial data helps you make informed decisions about whether prescription weight loss treatment might be suitable for you. Use our free BMI calculator above to check your current BMI against NHS eligibility thresholds.
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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.
SURMOUNT Trial Data and NHS Eligibility in the UK
The SURMOUNT trials were three pivotal clinical studies that tested Mounjaro's safety and effectiveness in adults with obesity or overweight with weight-related health conditions. SURMOUNT-1, the primary trial, included over 2,500 participants across multiple countries including the UK. Over 72 weeks, participants on the maximum 15 mg Mounjaro dose lost an average of 20.9% of their body weight, compared to just 3.3% in the placebo group. Results at 10 mg showed approximately 19.5% average loss, and at 5 mg approximately 15% loss.
These results led to NICE approval of tirzepatide for NHS weight management services in eligible adults. Current NHS UK eligibility includes adults with a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with weight-related health conditions such as type 2 diabetes, hypertension, or dyslipidaemia. For South Asian, Chinese, Black African, and Black Caribbean adults, lower BMI thresholds apply (27.5 kg/m² and above) due to higher metabolic disease risk at lower weights.
- 72-week trial duration showed sustained weight loss
- Results achieved alongside reduced-calorie diet and physical activity
- Individual weight loss varied significantly between participants
- Most common side effects were nausea, diarrhoea, and constipation — often decreased with time
Clinically BackedWeight Loss
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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.
NHS Access Routes and What Trial Data Means for You
NHS access to Mounjaro follows the SURMOUNT trial evidence through specialist tier 3 weight management services — not standard GP prescription. You'll be referred by your GP if eligible, assessed by a specialist team, and prescribed within NHS guidelines. Wait times vary significantly by region (ICB area), ranging from several months to over a year in some areas. Trial data showed weight loss required consistent use alongside lifestyle changes — medication is not a standalone solution.
The SURMOUNT results demonstrate that GIP/GLP-1 dual receptor agonists (Mounjaro's mechanism) may be more effective than single GLP-1 agonists for weight management. However, individual results vary — some participants lost significantly more or less than the average. Try our free GLP-1 weight loss calculator above to estimate potential outcomes at different doses based on clinical trial data. Your prescriber will discuss realistic expectations for your personal situation during clinical assessment.
- 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 was the SURMOUNT clinical trial?
SURMOUNT was a series of clinical trials testing Mounjaro (tirzepatide) for weight management. SURMOUNT-1 involved over 2,500 participants and showed average weight loss of 15–21% over 72 weeks depending on dose, supporting NICE approval for NHS use in the UK.
How much weight loss did Mounjaro show in the SURMOUNT trial?
At the maximum 15 mg dose, participants lost an average of 20.9% body weight over 72 weeks. At 10 mg, average loss was 19.5%, and at 5 mg approximately 15%. Results varied between individuals and were achieved alongside diet and exercise changes.
Does the SURMOUNT trial data mean I'll lose the same amount?
No — individual results vary significantly. The SURMOUNT figures are averages. Some participants lost more, others less. Your prescriber will discuss realistic expectations for you based on your individual health, starting weight, and lifestyle factors.
Why did NICE approve Mounjaro based on the SURMOUNT trial?
The SURMOUNT trials demonstrated that Mounjaro is both effective and safe for weight management in eligible adults. The sustained weight loss, reduced weight-related health risks, and acceptable safety profile met NICE's approval criteria for NHS prescription.
How does Mounjaro's SURMOUNT trial data compare to other weight loss injections?
Mounjaro is a dual GIP/GLP-1 agonist, while some alternatives (like Wegovy) are single GLP-1 agonists. Clinical trial data suggests Mounjaro may achieve slightly higher average weight loss, though individual responses vary considerably between medications and individuals.
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.