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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Tirzepatide and NICE: Mounjaro vs Wegovy Explained
Tirzepatide (Mounjaro) and semaglutide (Wegovy) are both NICE-approved GLP-1 receptor agonist medications for weight management in UK adults. The key difference is that tirzepatide is a dual GIP receptor and GLP-1 agonist, while Wegovy targets GLP-1 only. Both are prescription-only medicines available through NHS specialist services or private prescribing following clinical assessment. This guide compares the two medications to help you understand how they differ and what the clinical evidence shows.
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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.
Clinical Trial Evidence and Weight Loss Outcomes
Mounjaro (tirzepatide) was studied in the SURMOUNT-1 trial with impressive results: participants on the 15mg weekly weight loss injection lost an average of 20.9% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity. The 10mg dose achieved approximately 19.5% average weight loss.
Wegovy (semaglutide) demonstrated results in the STEP-1 trial: average weight loss of 14.9% body weight at the maximum 2.4mg dose over 68 weeks, also with lifestyle changes.
- Mounjaro: up to 20.9% average body weight loss (15mg dose)
- Wegovy: up to 14.9% average body weight loss (2.4mg dose)
- Both: individual results vary significantly
- Both: require reduced-calorie diet and physical activity for best outcomes
These are clinical trial averages. Your personal results may differ based on adherence, lifestyle factors, and individual metabolism. A prescriber will help determine which medication may be more suitable after clinical assessment.
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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.
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Mechanism, Dosing, and Suitability for Your Situation
The fundamental difference is mechanism: tirzepatide activates both GIP and GLP-1 pathways, while semaglutide (Wegovy) activates GLP-1 only. Both are prescription-only medicines requiring a Mounjaro KwikPen or Wegovy pen, both injected once weekly.
Dosing differs: Mounjaro ranges from 2.5mg to 15mg weekly; Wegovy from 0.25mg to 2.4mg weekly. Side effects are similar (nausea, diarrhoea, constipation) but individual tolerability varies.
Eligibility is the same for both: BMI ≥30, or BMI 27–29.9 with weight-related health conditions like type 2 diabetes, hypertension, or cardiovascular disease. Your GP or prescriber will assess which medication is appropriate after reviewing your medical history and current medications.
- 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 tirzepatide approved by NICE in the UK?
Yes. NICE has approved tirzepatide (Mounjaro) for weight management in UK adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions. It is available through NHS specialist tier 3 weight management services and through private GPhC-registered pharmacies following a clinical assessment by a UK-licensed prescriber.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist; Wegovy (semaglutide) is GLP-1 only. Clinical trials showed Mounjaro achieved higher average weight loss (~21% vs ~15%). Both are once-weekly injections, prescription-only, and require a clinical assessment before prescribing. Side effects are similar.
Can I use our BMI calculator to check my eligibility?
Yes. Use our free BMI calculator on this page to check your current BMI. If it's 30 or above, or 27–29.9 with weight-related health conditions, you may be eligible for either medication. However, a prescriber will make the final assessment based on your complete medical history.
Which medication should I choose — tirzepatide or semaglutide?
This depends on your individual health profile, medical history, and how you tolerate each medication. A prescriber will assess whether Mounjaro (tirzepatide) or Wegovy (semaglutide) is more suitable for you. Some people respond better to one over the other. Both require clinical assessment and prescription.
How do I access Mounjaro or Wegovy through the NHS?
You'll need referral to your local NHS tier 3 specialist weight management service from your GP. Availability and waiting times vary by region (ICB). Alternatively, both medications are available privately through GPhC-registered online pharmacies following an online consultation 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.