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 Studies and NHS Prescribing in the UK
The clinical evidence for Mounjaro (tirzepatide) comes from the SURMOUNT trials, which demonstrated significant weight loss across UK adult populations. Understanding these studies helps explain how Mounjaro is prescribed through NHS specialist services and why NICE has approved it for weight management. This guide covers the research behind Mounjaro, NHS eligibility criteria, and how the KwikPen injection is used as part of UK weight management pathways. Individual results vary, and prescription requires a clinical assessment from your GP or a licensed prescriber.
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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.
SURMOUNT Trials and Mounjaro Evidence in UK Practice
The SURMOUNT-1 clinical trial is the primary research supporting Mounjaro (tirzepatide) for weight management in the UK. Over 72 weeks, participants taking tirzepatide at various doses alongside a reduced-calorie diet and increased physical activity experienced average weight loss of 15% to 20.9% of their body weight — significantly more than the placebo group. The trial enrolled adults with a BMI of 30 or above, or 27 or above with weight-related health conditions, mirroring NHS eligibility criteria. Additional SURMOUNT trials (SURMOUNT-2 and SURMOUNT-3) confirmed these findings in people with type 2 diabetes and diverse ethnic backgrounds. Results showed dose-dependent effects: participants on the maximum 15 mg dose saw the greatest weight loss. Importantly, the trials also measured improvements in waist circumference and cardiometabolic markers. Use our GLP-1 weight loss calculator to explore how different doses might apply to your situation, and try the BMI calculator to understand your baseline.
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 Approval, NICE Guidance, and UK Prescribing Pathways
NICE has approved tirzepatide (Mounjaro) for NHS weight management, but access is through specialist tier 3 weight management services, not routine GP prescription. Your GP can refer you to a local specialist service if appropriate. The KwikPen injection is administered once weekly, with dose titration starting at 2.5 mg and escalating every four weeks up to a maximum of 15 mg. MHRA monitoring status means additional safety data is being collected. NHS access varies significantly by region and service availability, with waiting lists in some areas extending many months. Alternatively, tirzepatide is available through private prescription following an online clinical assessment with a UK-licensed prescriber. Both routes require a thorough health assessment to confirm eligibility and rule out contraindications.
- 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 did the SURMOUNT-1 trial show about Mounjaro weight loss?
SURMOUNT-1 demonstrated that participants on tirzepatide lost an average of 15% to 20.9% of body weight over 72 weeks, depending on dose, when combined with a reduced-calorie diet and increased physical activity. Results were significantly greater than placebo. Individual results vary.
Is Mounjaro available on the NHS in the UK?
Yes, NICE has approved tirzepatide for NHS weight management through specialist tier 3 services. Access requires a GP referral and varies by region. Waiting lists can be lengthy. Mounjaro is also available privately through online prescription services.
How does the SURMOUNT trial data compare to real-world UK prescribing?
SURMOUNT trials enrolled participants meeting NHS eligibility criteria (BMI 30+, or 27+ with comorbidities), so results are relevant to UK practice. However, real-world outcomes may vary. Your GP or prescriber can discuss how trial evidence applies to your situation.
What is the KwikPen and how is Mounjaro dosed based on the studies?
The KwikPen is Mounjaro's pre-filled injection device. Dosing starts at 2.5 mg weekly, increasing every four weeks. SURMOUNT trials used doses up to 15 mg. Maximum therapeutic dose is 15 mg once weekly.
How do Mounjaro studies relate to MHRA and UK safety monitoring?
Mounjaro carries MHRA Black Triangle (▼) status, meaning additional safety monitoring is ongoing. UK prescribers and patients report adverse events to support ongoing safety data collection beyond the original clinical trials.
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.