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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Expected Weight Loss With Mounjaro in the UK
Mounjaro (tirzepatide) is a prescription-only weight loss injection licensed in the UK that can help adults with obesity or overweight manage their weight more effectively. Clinical trial data shows adults using Mounjaro lost an average of 15–21% of their body weight over 72 weeks, though individual results vary significantly. Weight loss depends on dose, adherence, diet, physical activity, and personal factors. This guide explains what the research shows, NHS eligibility criteria, and how to access Mounjaro through specialist services or private prescribing in the UK. Use our free GLP-1 weight loss calculator above to estimate potential outcomes at different doses.
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Calculate Your BMI Instantly
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 Weight Loss Results — What Clinical Trials Show
The SURMOUNT-1 clinical trial tested Mounjaro's effectiveness in adults with obesity. Participants taking the maximum dose of 15 mg once weekly lost an average of 20.9% of their body weight over 72 weeks — roughly one year and a half. Those on 10 mg lost approximately 19.5%, and those on the lower 5 mg dose lost around 15%. However, these results were achieved alongside a reduced-calorie diet and increased physical activity, and individual weight loss varied considerably.
- 15 mg dose: ~20.9% average weight loss (72 weeks)
- 10 mg dose: ~19.5% average weight loss
- 5 mg dose: ~15% average weight loss
It's important to understand that these are trial averages — some people lost more, others less. Results also depend on dose titration speed, how your body responds, adherence to the injections, and whether you combine treatment with dietary and lifestyle changes. This is why your expected weight loss is unique to you.
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 Eligibility and Access to Mounjaro in the UK
NHS eligibility criteria: You may qualify for Mounjaro through NHS specialist tier 3 weight management services if you have a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower thresholds apply. NHS access involves referral from your GP to a specialist multidisciplinary weight management service — availability and waiting times vary significantly by region (Integrated Care Board). Alternatively, Mounjaro is available privately through GPhC-registered pharmacies following an online assessment with a UK-licensed prescriber, without requiring NHS referral. Check your eligibility and track progress using our free BMI calculator and weight loss calculator.
- 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 much weight can I realistically lose on Mounjaro?
Clinical trials showed average weight loss of 15–21% of body weight at 72 weeks, depending on dose. However, individual results vary — some people lose more, others less. Your actual weight loss depends on your starting weight, dose, adherence, diet, physical activity, metabolism, and personal factors. Your prescriber can give personalised expectations based on your health profile.
Is Mounjaro available on the NHS in the UK?
Yes, Mounjaro is approved by NICE and available through NHS tier 3 specialist weight management services. You need referral from your GP. Availability and waiting times vary by region — some areas have long waiting lists. Private access is available through online prescribing without NHS referral.
What dose of Mounjaro produces the best weight loss?
The maximum dose of 15 mg once weekly showed the highest average weight loss (~20.9%) in clinical trials. However, lower doses (5–10 mg) still produce significant results (15–19.5%). Your prescriber will start you on 2.5 mg and gradually increase based on tolerability and response, as lower doses have fewer side effects.
How does Mounjaro weight loss compare to Wegovy?
Both are prescription-only GLP-1 medications. Mounjaro (tirzepatide) is a dual GIP+GLP-1 agonist showing average weight loss of 15–21%. Wegovy (semaglutide) is a GLP-1 agonist showing average weight loss of ~15%. Mounjaro's dual mechanism may offer slightly better results on average, but individual outcomes vary. Your prescriber can advise which is suitable for you.
Does weight come back after stopping Mounjaro?
Weight loss from Mounjaro is not permanent — if you stop the injection without maintaining dietary and lifestyle changes, weight regain is common. Long-term weight management typically requires sustained behaviour change. Some people continue Mounjaro long-term under medical supervision, while others transition to maintenance through diet and exercise alone.
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.