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 vs Wegovy on the NHS — What's the Difference?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections available in the UK through NHS specialist services and private prescribing. While they work similarly, they use different mechanisms and showed different results in clinical trials. Understanding how they compare can help you discuss options with your GP or prescriber. Use our free GLP-1 weight loss calculator to explore potential outcomes with either medication, and our BMI calculator to assess your current health status.
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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.
How Mounjaro and Wegovy Work Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two separate hormone pathways. This dual mechanism may help regulate appetite more effectively and support feeling fuller after smaller meals. Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single hormone pathway.
In the SURMOUNT-1 clinical trial, adults on Mounjaro 15 mg (the maximum dose) lost an average of 20.9% of body weight over 72 weeks. In the STEP-1 trial, adults on Wegovy 2.4 mg (maximum dose) lost an average of 14.9% of body weight over 68 weeks. However, individual results vary significantly, and both medications are used alongside 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.
NHS Access, Eligibility, and Prescriber Choice
Both medications are available through NHS specialist tier 3 and tier 4 weight management services following referral from your GP. Eligibility requires a BMI of 30 or above, or 27 or above with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Your prescriber will assess which medication suits your individual health needs, medical history, and any other medications you take. Neither is assured to work — response varies between individuals. Both require ongoing monitoring and support from your healthcare team.
- 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 on the NHS?
Clinical trials showed higher average weight loss with Mounjaro, but individual results vary considerably. Your prescriber will recommend based on your personal health profile, not trial averages. Both are effective for many people; suitability depends on your individual circumstances.
Can I switch from Wegovy to Mounjaro on the NHS?
Switching between medications is possible but requires prescriber agreement and medical review. Your GP or specialist will assess whether a switch is clinically appropriate. Any change involves a reassessment period and dose adjustment, so discuss with your healthcare team first.
How long does it take to see results with either medication on the NHS?
Weight loss typically begins within the first 4 weeks, but most significant results appear after 12–16 weeks. Both medications require consistent use alongside lifestyle changes. Patience and adherence are key — results improve over months, not weeks.
Do both Mounjaro and Wegovy have the same side effects?
Both cause similar common side effects including nausea, diarrhoea, constipation, and stomach pain. These usually improve within weeks as your body adjusts. Rare serious side effects are possible with both. Your prescriber will discuss risks and monitor you throughout treatment.
What's the difference between Mounjaro and Ozempic?
Mounjaro is licensed for weight loss; Ozempic is licensed for type 2 diabetes at lower doses. Although both are semaglutide-based injections, Wegovy is the weight loss licensed version. Always use the medication prescribed to you — they are not interchangeable.
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.