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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Key Facts About Mounjaro in the UK
Mounjaro (tirzepatide) is a prescription-only, once-weekly injectable medicine approved in the UK for weight management in adults. It's a dual GIP and GLP-1 receptor agonist, meaning it works on two natural hormone pathways to help regulate appetite and support feeling fuller after meals. NHS NICE has approved tirzepatide for use within specialist weight management services. This guide covers the key facts about eligibility, how it works, NHS access, and what to expect. Use our free BMI calculator above to check your personal BMI and understand your eligibility context.
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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.
NHS Eligibility and Prescribing Facts
NHS eligibility criteria for Mounjaro: You may be eligible if you have a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, prediabetes, high blood pressure, abnormal blood fats, obstructive sleep apnoea, or cardiovascular disease history. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, NHS guidelines recommend lower BMI thresholds — eligibility may start at BMI 27.5 or above, as these populations face higher metabolic health risks at lower weights.
NHS access route: Mounjaro is prescribed through tier 3 specialist weight management services, not standard GP prescription. You'll need an NHS referral from your GP, followed by assessment by a multidisciplinary team. Availability varies significantly by region (ICB), and waiting lists can be substantial. NICE guidance approves tirzepatide use, but supply and access remain limited in many areas due to NHS budget constraints.
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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.
How Mounjaro Works and Key Clinical Data
Mounjaro is a dual GIP and GLP-1 receptor agonist. Unlike single-pathway medications, it activates two hormone systems that regulate appetite, blood sugar, and fat metabolism. The SURMOUNT-1 clinical trial showed average weight loss of 15–21% of body weight at the highest dose (15 mg) over 72 weeks, alongside reduced-calorie diet and increased physical activity. Results vary significantly between individuals. It's supplied as a pre-filled KwikPen containing 4 doses (4 weeks supply), with doses ranging from 2.5 mg to 15 mg weekly. Try our GLP-1 weight loss calculator to estimate potential results at different doses based on your current weight.
- 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 for weight loss?
Yes, NICE has approved tirzepatide (Mounjaro) for NHS weight management. However, access is through specialist tier 3 services only, not standard GP prescription. You need an NHS referral and a waiting list applies. Availability varies by region. Private prescription routes may offer faster access.
What's the difference between Mounjaro and Wegovy in the UK?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist; Wegovy (semaglutide) is GLP-1 only. Both are once-weekly injections approved in the UK. Clinical trials show Mounjaro may achieve slightly higher average weight loss (15–21% vs ~15% for Wegovy), but individual results vary. Both require prescription and clinical assessment.
Do I need to meet BMI thresholds to get Mounjaro on the NHS?
Yes. You'll typically need a BMI of 30 or above, or 27–29.9 with weight-related health conditions (diabetes, high blood pressure, cardiovascular disease, etc.). South Asian and Black heritage adults may qualify at BMI 27.5 or above. Your GP can discuss whether you meet NHS eligibility in your region.
What does "tirzepatide" mean?
Tirzepatide is the active ingredient in Mounjaro. It's the chemical name for the medicine. You may see it referred to as either "tirzepatide" or "Mounjaro" — they're the same drug. The brand name Mounjaro is used in the UK, whilst tirzepatide is the generic name.
How long does Mounjaro take to work?
Weight loss typically begins within the first 4 weeks, though it accelerates over weeks 5–12 as your body adjusts to each dose increase. The medication is titrated gradually over 5+ months from 2.5 mg to maintenance dose. Maximum weight loss effects are usually seen around weeks 16–20. Use our progress tracker to log weekly changes and monitor your individual response.
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.