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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How Many People Are On Mounjaro In The UK?
Exact figures on how many UK adults currently use Mounjaro are not publicly available, but prescription data suggests uptake has grown significantly since NICE approval. Both Mounjaro and Wegovy are increasingly prescribed through NHS specialist weight management services and private online prescribing. Understanding the difference between these two prescription weight loss injections can help you and your GP decide which might be suitable for you.
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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 — Trial Data and Mechanism
Mounjaro (tirzepatide) and Wegovy (semaglutide) are the two most commonly prescribed GLP-1 based weight loss injections in the UK, but they work through different mechanisms. Mounjaro is a dual GIP and GLP-1 receptor agonist, activating two hormone pathways simultaneously, while Wegovy is a GLP-1 agonist only. Clinical trial data shows the difference: in the SURMOUNT-1 trial, Mounjaro at maximum dose (15 mg) achieved average weight loss of approximately 20.9% of body weight. Wegovy's STEP-1 trial showed average weight loss of approximately 14.9% at the maximum dose (2.4 mg). However, individual results vary significantly, and clinical trial populations do not represent all users. Both require a reduced-calorie diet and increased physical activity for best results.
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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.
Prescription Access In The UK — NHS And Private Routes
Both Mounjaro and Wegovy are prescription-only medicines in the UK and require a clinical assessment before prescribing. NHS access is through tier 3 specialist weight management services, typically requiring a GP referral. Availability and waiting times vary significantly by region (ICB). Private prescribing is available through GPhC-registered online pharmacies following an online clinical consultation — this route does not require NHS referral. A licensed prescriber will assess your BMI, medical history, and weight-related health conditions to determine eligibility. Your prescriber will then recommend which medication, if any, is most suitable for your individual circumstances based on mechanism, dose titration schedule, and your personal health profile.
- 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 more effective than Wegovy in the UK?
Clinical trials suggest Mounjaro may produce slightly higher average weight loss (20.9% vs 14.9%), but individual results vary considerably. Effectiveness depends on your personal response, adherence, diet, and activity levels. Your prescriber will recommend the medication most suitable for you based on your health profile, not just trial averages.
How many UK adults are prescribed Mounjaro?
Exact figures are not publicly available. Prescription data is not routinely published by NHS England or MHRA. Both Mounjaro and Wegovy uptake has grown since licensing, but specific user numbers remain proprietary to manufacturers and prescribing services.
What's the difference between Mounjaro's mechanism and Wegovy's?
Mounjaro activates both GIP and GLP-1 hormone pathways (dual action), while Wegovy activates GLP-1 only (single action). This mechanistic difference may explain the different trial weight loss outcomes, though prescriber choice also depends on side effect tolerance and your medical history.
Can I switch from Wegovy to Mounjaro on the NHS?
Switching between medications requires your prescriber's approval and clinical reassessment. Approximate dose equivalences exist (e.g., Wegovy 2.4 mg ≈ Mounjaro 15 mg), but any switch must be managed individually by your NHS specialist or private prescriber, not self-initiated.
Which weight loss injection should I choose?
That's a decision for you and your prescriber following a full clinical assessment. Factors include your BMI, weight-related health conditions, tolerance to side effects, injection frequency preference, NHS availability, and cost. Neither medication is universally "better" — suitability is individual. Use our free GLP-1 weight loss calculator to explore potential outcomes with different medications.
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.