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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How Long Has Mounjaro Been Tested in the UK?
Mounjaro (tirzepatide) has been clinically tested for weight management since the SURMOUNT trials began in 2021, with results published through 2023. The medication received MHRA approval in the UK in December 2023 for weight management in adults. This guide explains the clinical evidence behind Mounjaro, how long it's been tested, and how you can access it in the UK through NHS or private routes following a proper 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.
Mounjaro Clinical Trial Timeline and Evidence
Mounjaro (tirzepatide) underwent extensive clinical testing before UK approval. The SURMOUNT programme comprised three major randomised controlled trials conducted between 2021 and 2023, involving over 2,500 participants globally. SURMOUNT-1, the primary efficacy trial, showed that participants on tirzepatide lost an average of 15–21% of body weight over 72 weeks, depending on dose (5 mg, 10 mg, or 15 mg), alongside reduced-calorie diet and increased physical activity. Results were published in the New England Journal of Medicine in 2022. The MHRA granted approval in December 2023 following review of this clinical data. Mounjaro currently carries Black Triangle (▼) status, meaning it remains under additional monitoring in the UK — a standard precaution for newer medications. This does not indicate safety concerns but rather that the regulator continues to monitor long-term safety data as more people use the medication in real-world settings.
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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.
Accessing Mounjaro in the UK: NHS vs Private Routes
In the UK, NICE has approved tirzepatide for NHS use within specialist tier 3 and 4 weight management services. However, NHS access is limited and varies significantly by region. Many areas have waiting lists of several months to over a year. Private prescription routes are available through UK-licensed online prescribers who conduct remote clinical assessments. Following assessment, prescriptions are dispensed by GPhC-registered pharmacies. Costs typically range from £129 to £320 per month depending on dose. Use our free GLP-1 weight loss calculator to estimate potential outcomes, and consult your GP about which access route suits your situation. Your prescriber will assess eligibility based on your BMI, health conditions, and medical history.
- 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.
How long have clinical trials for Mounjaro been running?
Mounjaro (tirzepatide) underwent the SURMOUNT clinical trial programme from 2021 to 2023, with results published in major medical journals. The MHRA approved it in December 2023. Real-world monitoring continues via Black Triangle status, so safety data is building constantly as more UK patients use it.
Is Mounjaro available on the NHS in the UK?
Yes, NICE has approved tirzepatide for NHS specialist weight management services (tier 3–4). However, availability and waiting times vary significantly by region. Many areas have long waiting lists. Your GP can refer you to your local specialist service to discuss eligibility and timelines.
How much does Mounjaro cost on prescription in the UK?
Private prescription costs typically range from £129 to £320 per month depending on dose (2.5 mg to 15 mg). This does not include prescriber consultation fees. NHS provision is free, but access is limited and varies by region. Always check current pricing with your prescriber.
What does SURMOUNT-1 tell us about Mounjaro effectiveness?
SURMOUNT-1 showed participants lost an average of 15–21% body weight over 72 weeks, depending on dose. Individual results varied significantly. Weight loss was achieved alongside a reduced-calorie diet and increased physical activity — the medication alone is not sufficient without lifestyle changes.
What is Black Triangle status and why does Mounjaro have it?
Black Triangle (▼) means the MHRA is monitoring the medication extra carefully for new safety signals. This is routine for newer drugs and does not indicate a safety problem — it reflects standard regulatory practice to protect patient safety as more data accumulates.
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.