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 Comparison: How It Stacks Up in the UK
If you're considering Mounjaro for weight management in the UK, it helps to understand how it compares to other available options. Mounjaro (tirzepatide) is a prescription-only injection that works differently from other weight loss medications, and your eligibility, access route, and outcomes may vary depending on your circumstances. This guide compares Mounjaro with Wegovy, Saxenda, and lifestyle-based approaches, with a focus on NHS guidance, NICE recommendations, and what's actually available to UK adults. Use our free BMI calculator above to check where you currently sit on the UK health spectrum, and our GLP-1 weight loss calculator to explore potential outcomes with different medications.
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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 vs Wegovy: Key Differences for UK Patients
Mounjaro (tirzepatide) and Wegovy (semaglutide) are the two most commonly prescribed GLP-1-based weight loss injections in the UK, but they work via different mechanisms. Mounjaro is a dual GIP and GLP-1 receptor agonist — meaning it activates two natural hormone pathways — whilst Wegovy is a GLP-1 agonist only. In clinical trials, Mounjaro showed slightly higher average weight loss (around 20.9% at the maximum 15mg dose) compared to Wegovy (around 14.9% at 2.4mg), though individual results vary significantly. Both require a UK prescription following a clinical assessment, and both can be accessed either through NHS specialist tier 3 weight management services or privately via online prescribing. The Mounjaro KwikPen is pre-filled and injected once weekly, with dose titration starting at 2.5mg and escalating to a maximum of 15mg. Wegovy uses a gentler escalation from 0.25mg to 2.4mg. Neither medication is assured to produce specific weight loss outcomes — they're prescription-only tools that work best alongside reduced-calorie diet and increased physical activity.
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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, NICE Guidance, and Private Routes in the UK
NHS access to Mounjaro is through specialist tier 3 weight management services, following NICE recommendations. You'll typically need a GP referral and meet specific criteria: BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, hypertension, or sleep apnoea. For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds apply (from 27.5 and above). NHS waiting lists vary significantly by region — some areas have waits of several months or longer. Private access is faster: you complete an online clinical assessment with a UK-licensed prescriber, and if approved, receive a prescription dispensed by a GPhC-registered pharmacy. Private costs range from approximately £129–£320 per month depending on dose. Both routes require an actual prescription — Mounjaro is not available over the counter or without clinical assessment, and MHRA monitoring applies.
- 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 Mounjaro available on the NHS in the UK?
Yes, Mounjaro is available through NHS specialist tier 3 weight management services following NICE approval. However, NHS access requires a GP referral, specific eligibility criteria, and availability varies significantly by region. Many areas have waiting lists of several months. Private prescribing offers faster access without NHS referral.
How does Mounjaro compare to Wegovy in clinical trials?
In clinical trials, Mounjaro showed average weight loss of around 20.9% at the maximum 15mg dose, whilst Wegovy showed around 14.9% at 2.4mg. However, individual results vary widely, and both are prescription-only medications requiring clinical assessment and lifestyle changes for best results.
What's the difference between Mounjaro and Saxenda?
Mounjaro (tirzepatide, dual mechanism) and Saxenda (liraglutide, GLP-1 only) are both UK-licensed for weight management. Mounjaro is once-weekly injection, Saxenda is once-daily. Mounjaro typically shows higher average weight loss in trials, but Saxenda is longer-established in the UK market. Both require prescription and clinical assessment.
Can I get Mounjaro privately if I don't qualify for NHS?
Yes. Private weight loss prescribing is available through online consultations with UK-licensed prescribers. If clinically appropriate, you'll receive a prescription dispensed by a GPhC-registered pharmacy. This route is faster than NHS but not covered by the NHS and costs vary by provider and dose.
What NHS criteria do I need to meet for Mounjaro?
NHS eligibility typically requires BMI of 30 or above, or 27–29.9 with weight-related health conditions (diabetes, hypertension, sleep apnoea). For South Asian, Chinese, Black African, or Black Caribbean adults, thresholds start from 27.5. Your GP can assess your eligibility and refer to local specialist tier 3 services. Use our free BMI calculator to check your starting point.
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.