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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Wegovy Or Mounjaro — Which Is Right For You In The UK?
If you're considering weight loss medication in the UK, you've likely come across both Wegovy and Mounjaro. Both are prescription-only GLP-1 based injections approved for weight management, but they work slightly differently and have different access routes through the NHS. Understanding the differences, eligibility criteria, and how to access them through specialist services can help you and your GP make an informed decision. Use our free GLP-1 weight loss calculator to explore potential outcomes with either medication.
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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.
NHS Eligibility And Prescribing Guidelines
Both Wegovy (semaglutide) and Mounjaro (tirzepatide) are licensed for weight management in UK adults and eligible through NHS specialist tier 3 weight management services. Eligibility criteria are identical for both medications:
- BMI of 30 kg/m² or above, OR
- BMI of 27–29.9 kg/m² with at least one weight-related health condition (type 2 diabetes, high blood pressure, dyslipidaemia, obstructive sleep apnoea, or cardiovascular disease)
- Lower thresholds apply for adults of South Asian, Chinese, Black African, or Black Caribbean heritage (BMI 27.5+)
NICE guidance supports both medications as part of a comprehensive weight management approach alongside reduced-calorie diet and increased physical activity. Access is through NHS specialist services following referral from your GP, though waiting lists vary significantly by region. Clinical trials (STEP for Wegovy, SURMOUNT for Mounjaro) showed average weight losses of approximately 15% and 15–21% of body weight respectively, though individual results vary considerably.
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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.
Wegovy Vs Mounjaro — Key Clinical Differences
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, activating two hormone pathways simultaneously, which may explain its slightly higher average weight loss in clinical trials compared to Wegovy. Wegovy (semaglutide) activates only the GLP-1 pathway. Both are once-weekly injections, but Mounjaro uses a KwikPen device while Wegovy uses an auto-injection pen. Mounjaro requires 4 weeks on each dose before escalation, whereas Wegovy escalates weekly. Common side effects overlap (nausea, diarrhoea, constipation, vomiting) but may vary in severity between individuals. Your prescriber will assess which medication suits your health profile, preferences, and any other medications you take. Calculate your estimated weight loss with our GLP-1 weight loss calculator to see potential outcomes at different doses.
- 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.
Can I get Wegovy or Mounjaro through the NHS?
Yes, both medications are available through NHS specialist tier 3 weight management services. You'll need a referral from your GP. Access depends on your BMI, health conditions, and your local NHS Integrated Care Board's funding availability. Waiting lists can be lengthy in many areas (months to years). Some regions have better access than others, so ask your GP about local provision.
What's the main difference between Wegovy and Mounjaro?
Mounjaro (tirzepatide) is a dual GIP + GLP-1 agonist, activating two hormone pathways, whereas Wegovy (semaglutide) activates only GLP-1. Clinical trials suggest Mounjaro may produce slightly higher average weight loss (15–21% vs 15%), but individual results vary. Both are once-weekly injections with similar side effect profiles.
How long does it take to get Wegovy or Mounjaro on the NHS?
There's no fixed timeline. After GP referral, you'll be added to your local specialist weight management service waiting list. Some areas have waits of several months; others may wait 1–2 years. Private prescribing routes are typically faster (2–4 weeks), though at personal cost. Ask your GP about current waiting times in your area.
What's the difference between Mounjaro KwikPen and Wegovy's auto-injector?
Mounjaro comes in a reusable KwikPen that clicks to deliver each dose; Wegovy uses a pre-filled auto-injection pen. Both are single-dose weekly injections. KwikPen requires you to attach a new needle weekly, while Wegovy's pen has the needle integrated. Both are simple to use; preference is personal.
Will the NHS prescribe Wegovy or Mounjaro if I have type 2 diabetes?
Yes. Having type 2 diabetes or prediabetes is a weight-related health condition that can support eligibility even if your BMI is 27–29.9. Your prescriber will assess overall suitability. If you're already taking diabetes medications (especially insulin or sulphonylureas), dose adjustments may be needed when starting a GLP-1 medication.
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.