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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What's the Difference Between Wegovy and Mounjaro?
Wegovy and Mounjaro are both prescription-only weight management injections available in the UK, but they work differently and have distinct costs and access routes. Wegovy (semaglutide) is a GLP-1 receptor agonist, while Mounjaro (tirzepatide) uses a dual GIP and GLP-1 mechanism. Understanding the differences—including how they're dosed, what they cost privately, and how to access them through the NHS—can help you make an informed decision with your GP or prescriber. Both require clinical assessment before prescription, and both are used alongside lifestyle changes for best results.
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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.
How Wegovy and Mounjaro Differ: Mechanism, Dosing & Results
Mechanism: Wegovy activates only the GLP-1 hormone pathway to reduce appetite and promote fullness. Mounjaro (tirzepatide) activates both GIP and GLP-1 pathways simultaneously, which may offer a dual approach to appetite control and metabolic regulation.
Dosing schedules: Both are once-weekly injections. Wegovy starts at 0.25 mg and titrates to a maximum of 2.4 mg over 16+ weeks. Mounjaro begins at 2.5 mg and escalates to a maximum of 15 mg over 20+ weeks, with more dose options available.
Clinical trial results: In STEP-1 trials, Wegovy helped participants lose approximately 15% body weight on average. SURMOUNT-1 trials showed Mounjaro participants lost 15–21% body weight on average—though individual results vary significantly. Both results were achieved alongside reduced-calorie diet and increased physical activity.
Injection device: Wegovy uses a pre-filled auto-injection pen; Mounjaro uses a pre-filled KwikPen device.
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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.
UK Costs: Private Prescription Prices & NHS Access Routes
Private prescription costs: Wegovy typically costs £129–£250 per month depending on dose and prescription provider. Mounjaro private prescriptions generally range from £149–£320 per month at higher doses. Prices vary between online prescribing services; always check current pricing with your chosen provider before committing.
NHS access: Both medications are available through NHS specialist tier 3 weight management services, but access is highly variable by region and involves GP referral. Waiting lists can extend many months. Private online consultation offers faster access without NHS referral, requiring a clinical assessment from a UK-licensed prescriber and dispensing by a GPhC-registered pharmacy. Use our free GLP-1 weight loss calculator to explore projected results with either medication.
- 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.
Which one causes more weight loss—Wegovy or Mounjaro?
Clinical trials suggest Mounjaro (tirzepatide) may result in slightly greater average weight loss (15–21%) compared to Wegovy (approximately 15%), but individual results vary substantially. Your personal response depends on genetics, lifestyle adherence, dose tolerance, and other health factors. Always discuss expected outcomes realistically with your prescriber.
Can I switch from Wegovy to Mounjaro on the NHS?
Switching between medications is possible but requires prescriber guidance. If you're accessing through an NHS specialist service, discuss any concerns about effectiveness or side effects with your specialist team. They can advise whether switching is appropriate for you based on your response to the current medication.
Is Mounjaro cheaper than Wegovy in the UK?
Costs vary by provider and dose. Wegovy typically ranges £129–£250/month; Mounjaro £149–£320/month. At lower Mounjaro doses (2.5–5 mg), costs may be similar to Wegovy. At maximum doses, Mounjaro can be more expensive. Always compare current pricing across GPhC-registered online pharmacies before prescribing.
How long does it take to see results with either medication?
Most people notice appetite reduction within 1–2 weeks of starting. Measurable weight loss typically becomes evident by 4–6 weeks, though this varies. Both medications work best when combined with consistent calorie deficit and physical activity. Use our BMI calculator to track changes alongside our free progress tracker.
Do I need a GP referral to get Wegovy or Mounjaro privately?
No. Private online prescribers can issue prescriptions directly following a clinical consultation—no NHS GP referral required. However, informing your GP is advisable for safety, especially if you take other medications. NHS access does require GP referral to a specialist weight management service.
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.