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 Take Mounjaro — Comparing UK GLP-1 Weight Loss Medications
Mounjaro (tirzepatide) has become increasingly popular for weight management in the UK since its approval, but exact UK usage figures are not publicly available. What we do know comes from clinical trial data and NHS prescribing trends. Both Mounjaro and Wegovy (semaglutide) are prescription-only weight loss injections, and choosing between them depends on individual health factors assessed during a clinical consultation. This guide compares real trial data, eligibility, and what drives prescriber decisions between these two medications.
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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.
Clinical Trial Data: SURMOUNT vs STEP — What the Numbers Show
Mounjaro (tirzepatide) was tested in the SURMOUNT-1 trial with approximately 2,500 participants over 72 weeks. At the maximum 15 mg dose, participants achieved an average weight loss of 20.9% of their body weight. The SURMOUNT trials demonstrated that tirzepatide's dual GIP and GLP-1 receptor agonist mechanism produced slightly higher average weight loss than single GLP-1 agonists.
Wegovy (semaglutide) was tested in the STEP-1 trial with approximately 1,900 participants over 68 weeks. At the maximum 2.4 mg dose, participants achieved an average weight loss of approximately 15% of their body weight. Semaglutide activates the GLP-1 pathway only, which is why results differed from tirzepatide's dual mechanism.
Both trials included participants with a BMI over 30 or BMI 27–29.9 with weight-related health conditions, using reduced-calorie diets and increased physical activity. Individual results varied considerably in both trials — some people lost more, some less.
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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.
Why Prescribers Choose One Over the Other — Individual Suitability Matters
Neither medication is universally "better" — prescriber choice depends on your personal health profile and response. Mounjaro eligibility in the UK follows the same BMI thresholds as Wegovy, and both require a clinical assessment by a licensed prescriber. Some GPs or specialist services may have preferred options based on availability, cost, or experience with side effects.
Your prescriber will consider your weight-related health conditions, other medications, and whether you've tried weight loss treatment before. Access through NHS specialist services varies significantly by region — some areas have long waiting lists. Private prescribing allows faster access following an online clinical assessment. Use our free GLP-1 weight loss calculator to explore projected outcomes at different doses, and our BMI calculator to assess your current starting point. Both tools can help your discussion with your prescriber.
- 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.
How many UK people currently take Mounjaro for weight loss?
Exact figures are not publicly disclosed, but NHS and private prescription data show rapid uptake since 2023. UK prescribing numbers are lower than for Wegovy historically, but Mounjaro uptake is increasing. Your prescriber can advise you based on current availability in your area.
Is Mounjaro more effective than Wegovy for weight loss?
Clinical trials show Mounjaro produced slightly higher average weight loss (20.9% vs 15% at maximum doses), but individual results vary significantly. Both are effective — the difference may not be meaningful for every person. Your prescriber will recommend based on your personal circumstances.
Why would a prescriber choose Mounjaro over Wegovy?
Reasons include dual GIP+GLP-1 mechanism, patient response patterns, side effect profile, regional availability, cost, or prior trial of other medications. Some patients tolerate one better than the other. Clinical assessment determines the best option for you.
Can I switch from Wegovy to Mounjaro if Wegovy doesn't work for me?
Yes, switching is possible and should be discussed with your prescriber. There is no official established conversion chart between the two medications — your prescriber will advise the appropriate starting dose and titration schedule if a switch is recommended.
Are Mounjaro and Wegovy both available on the NHS in the UK?
Both are NHS-approved for weight management, but access is through specialist tier 3 weight management services. Availability varies widely by region and ICB. Private prescribing offers faster access following an online clinical assessment with a UK-licensed prescriber.
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.