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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Average Mounjaro Weight Loss in the UK
Mounjaro (tirzepatide) is a prescription-only weekly injection licensed in the UK for weight management. Clinical trials showed average weight loss ranging from 15% to 21% of body weight over 72 weeks, though individual results vary significantly. On the NHS, access is through specialist tier 3 weight management services, where prescribers assess eligibility based on BMI and health conditions. This guide explains the evidence-based weight loss data, UK prescribing context, and what realistic expectations should be.
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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.
Average Weight Loss Data from Clinical Trials
The SURMOUNT-1 clinical trial — the main UK-relevant trial — followed 2,539 adults with a BMI of 27 or above. Over 72 weeks, participants receiving Mounjaro alongside a reduced-calorie diet and increased physical activity achieved:
- 5 mg dose: approximately 15% average body weight loss
- 10 mg dose: approximately 19.5% average body weight loss
- 15 mg dose: approximately 20.9% average body weight loss (maximum licensed dose)
Important context: these are average figures — some participants lost more, others less. Weight loss typically begins within 2–4 weeks and continues progressively as doses increase over the 16–20 week titration period. Results are dependent on consistent use, dietary changes, and physical activity. Using our free GLP-1 weight loss calculator can help you estimate potential weight loss at different doses based on your starting weight.
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 Specialist Prescribing
On the NHS, Mounjaro is prescribed through tier 3 specialist weight management services, not by standard GP prescription. You typically need a referral from your GP to access these services. NHS NICE guidance approves tirzepatide (Mounjaro) for adults with:
- BMI 30 kg/m² or above, OR
- BMI 27–29.9 kg/m² with weight-related health conditions (type 2 diabetes, hypertension, dyslipidaemia, sleep apnoea)
- Lower thresholds apply for South Asian, Chinese, Black African, and Black Caribbean adults (BMI 27.5+)
Availability varies significantly by region. Many NHS areas have lengthy waiting lists. Private prescribing through licensed UK prescribers offers faster access. Calculate your BMI using our free BMI calculator to understand your eligibility category and discuss options with your GP.
- 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 15–clinically studied weight loss realistic for everyone on Mounjaro?
No. The 15–21% figure is an average from clinical trials. Individual results vary — some people lose more, others lose less. Factors affecting results include starting weight, adherence to medication, diet quality, physical activity level, genetics, and medical conditions. Always discuss realistic expectations with your prescriber based on your personal health profile.
How long does it take to see weight loss on Mounjaro?
Weight loss typically begins within 2–4 weeks of starting the first dose (2.5 mg). However, most significant loss occurs as doses increase during the 16–20 week titration phase. Full results are usually observed by 12–16 weeks on your maintenance dose. Consistency is important — skipping doses slows progress.
What's the difference between SURMOUNT trial results and real-world NHS outcomes?
SURMOUNT trial participants received intensive support including structured diet, exercise coaching, and frequent check-ins. Real-world NHS outcomes may vary — some patients lose more, some less, depending on lifestyle adherence and individual factors. Your specialist team will monitor progress and adjust doses accordingly.
Can I lose more weight by increasing my Mounjaro dose beyond 15 mg?
No. 15 mg weekly is the maximum licensed dose in the UK. Increasing beyond this is not recommended and is not approved by the MHRA. If weight loss plateaus on 15 mg, your prescriber may explore other strategies like dietary review, activity increases, or combination treatments — not higher doses.
How does Mounjaro compare to Wegovy for average weight loss?
Clinical data shows Mounjaro at 15 mg achieved approximately 20.9% average weight loss, while Wegovy at 2.4 mg (maximum dose) achieved approximately 14.9% average weight loss in trials. However, these are different trials and direct comparisons are not perfect. Individual response varies. Your prescriber will advise which is more suitable for you.
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.