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 Is Wegovy Different From Mounjaro?
Wegovy and Mounjaro are both prescription-only weight management injections available in the UK, but they work through different mechanisms and have distinct dosing schedules. Understanding the key differences can help you and your GP or prescriber determine which option might be more suitable for your individual health situation. Both require a clinical assessment before prescription, and both are used alongside dietary changes and increased physical activity.
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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.
Key Differences in Mechanism and Clinical Data
Wegovy (semaglutide) is a GLP-1 receptor agonist — it activates a single natural hormone pathway (GLP-1) to help reduce appetite and support feeling fuller after smaller meals. In clinical trials (STEP-1), Wegovy helped participants lose an average of approximately 14.9% of their body weight over 68 weeks at the maximum dose of 2.4 mg.
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways simultaneously. This dual mechanism may provide additional support for appetite regulation and fat utilisation. In the SURMOUNT-1 clinical trial, Mounjaro resulted in average weight loss of approximately 15–21% of body weight, depending on dose, over 72 weeks. The maximum dose is 15 mg weekly, significantly higher than Wegovy's maximum.
- Dosing: Wegovy starts at 0.25 mg and escalates to 2.4 mg maximum. Mounjaro starts at 2.5 mg and escalates to 15 mg maximum.
- Injection frequency: Both are once-weekly injections.
- Individual results vary: Clinical trial averages do not predict personal outcomes — response depends on many factors including metabolism, lifestyle, and adherence.
Clinically BackedWeight Loss
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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.
Which Medication Is Right for You?
Neither Mounjaro nor Wegovy is universally "better" — suitability depends on your individual health profile, medical history, and how your body responds. Your GP or prescriber will assess your eligibility and recommend the most appropriate option during a clinical assessment. Both medications are available through NHS specialist tier 3 weight management services (with significant regional variation and waiting lists) or through private online prescribing following clinical consultation. Use our free GLP-1 weight loss calculator to explore projected outcomes at different doses, and try our BMI calculator to understand your current health baseline. Both injections require commitment to lifestyle changes for optimal results — medication alone is not a substitute for dietary adjustment and physical activity.
- 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?
Clinical trial data shows Mounjaro participants lost slightly more weight on average (15–21% vs 14.9%), but individual results vary significantly. Neither is universally more effective — response depends on your personal metabolism and adherence. Your prescriber will recommend the best option for you.
Can I switch from Wegovy to Mounjaro or vice versa?
Any switch between medications must be managed by your prescriber. There is no official NHS conversion chart between the two. Your prescriber will assess whether a switch is appropriate and determine a safe transition plan if needed.
Is Mounjaro the same as a Mounjaro KwikPen?
Mounjaro comes in a pre-filled KwikPen device — that's the standard way it's dispensed. The KwikPen contains the tirzepatide injection ready to use. Wegovy also comes as a pre-filled auto-injection pen, but they are not interchangeable devices.
How do I know which injection to ask my GP about?
You cannot choose which medication to receive — your GP or specialist prescriber will assess your health profile and recommend the most appropriate option based on your eligibility and medical history. Both are only available following clinical assessment and prescription.
Are both available on the NHS in the UK?
Both Mounjaro and Wegovy are approved for NHS prescription through specialist tier 3 weight management services, but availability varies significantly by region and ICB. Private prescribing is also available without NHS referral through GPhC-registered online pharmacies following clinical consultation.
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.