The UK's most complete GLP-1 guide
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- 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 — How Much Weight Loss Do They Help?
If you're considering Mounjaro or Wegovy for weight management, you're probably wondering how much weight loss each medication may help achieve and how their doses differ. Both are prescription-only GLP-1 receptor agonist medications licensed in the UK, but they work slightly differently and have different dosing schedules. This guide compares the clinical trial data, dosing ranges, and what these differences mean for your individual suitability — always determined by a prescriber following a clinical assessment.
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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.
Mounjaro vs Wegovy — Doses and Weight Loss Trial Results
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — meaning it activates two hormone pathways rather than one. In the SURMOUNT-1 clinical trial, participants taking the maximum 15mg dose lost an average of 20.9% of their body weight over 72 weeks. At 10mg, average loss was approximately 19.5%, and at 5mg approximately 15%. The KwikPen dose titration typically runs: 2.5mg weeks 1–4, 5mg weeks 5–8, 7.5mg weeks 9–12, 10mg weeks 13–16, 12.5mg weeks 17–20, then 15mg from week 21 onwards — minimum 4 weeks at each dose.
Wegovy (semaglutide) is a single GLP-1 receptor agonist. In the STEP-1 trial, participants on the maximum 2.4mg dose lost an average of 14.9% of body weight at 68 weeks. Wegovy's dose escalation is: 0.25mg weeks 1–4, 0.5mg weeks 5–8, 1mg weeks 9–12, 1.7mg weeks 13–16, then 2.4mg from week 17. Both require reduced-calorie diet and increased physical activity — medication works alongside lifestyle changes, not instead of them.
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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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Which Is Right for You? Individual Suitability and Prescriber Assessment
Because Mounjaro is a dual GIP+GLP-1 agonist (versus Wegovy's single GLP-1 mechanism), clinical trials suggest it may produce slightly greater average weight loss — but individual results vary significantly, and some people respond better to one medication than the other. Your prescriber will assess your personal health history, any existing medications, comorbidities, and preferences to determine which is more suitable. Both require a UK prescription, clinical assessment, and are available through NHS specialist tier 3 weight management services or private online prescribing. Try our free GLP-1 weight loss calculator to explore projected weight loss at different doses, and use the BMI calculator to check your starting point and target range for reference.
- 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 stronger than Wegovy for weight loss?
Clinical trials show Mounjaro (tirzepatide) produced average weight loss of 15–20.9% depending on dose, while Wegovy (semaglutide) averaged 14.9% at maximum dose. However, individual results vary significantly — some people respond better to one than the other. Your prescriber will recommend the most suitable option based on your personal health profile.
What is the maximum dose of Mounjaro compared to Wegovy?
Mounjaro's maximum dose is 15mg once weekly. Wegovy's maximum is 2.4mg once weekly. While Mounjaro doses are higher in numerical value, they work through different mechanisms (dual GIP+GLP-1 vs single GLP-1), so direct comparison by dose number is not meaningful. Effectiveness depends on individual response.
How long does it take to reach the full dose of each medication?
Mounjaro requires approximately 20–21 weeks to reach maximum 15mg dose (4 weeks minimum at each escalation step). Wegovy takes approximately 16–17 weeks to reach maximum 2.4mg dose. Both follow gradual titration to minimise side effects and allow your body to adjust.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching between the two requires prescriber guidance — there is no official conversion chart. Your GP or the prescriber assessing you will manage any switch based on your individual response and health factors. Never stop one medication and start another without medical supervision.
Which medication is available on the NHS in the UK?
Both Mounjaro and Wegovy are licensed for NHS use, but access is through tier 3 specialist weight management services and varies significantly by region and local ICB. Private prescribing via registered online pharmacies is also available for both. Ask your GP about NHS referral or contact a GPhC-registered pharmacy for private assessment options.
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