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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Average Monthly Weight Loss on Mounjaro vs Wegovy
Both Mounjaro and Wegovy are prescription weight loss injections available in the UK, but they work slightly differently and deliver different average weight loss results. Clinical trials show that Mounjaro (tirzepatide) typically produces greater weight loss than Wegovy (semaglutide) on average, though individual results vary significantly. Understanding the trial data and how these medications work can help you and your GP or prescriber decide which might be more suitable for you.
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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.
Clinical Trial Data: SURMOUNT vs STEP
Mounjaro (tirzepatide) was studied in the SURMOUNT-1 clinical trial over 72 weeks. At the maximum dose of 15 mg weekly, participants lost an average of approximately 20.9% of their body weight. At the 10 mg dose, average weight loss was around 19.5%. At the starting 5 mg dose, average loss was approximately 15%.
Wegovy (semaglutide) was studied in the STEP-1 trial over 68 weeks. At the maximum dose of 2.4 mg weekly, participants lost an average of approximately 14.9% of their body weight. This is notably lower than Mounjaro's results, though Wegovy still represents significant weight loss when combined with dietary changes and increased physical activity.
Translated to monthly terms, Mounjaro typically produces weight loss of approximately 1.5–2 kg per month on average at higher doses, while Wegovy typically produces approximately 0.8–1.5 kg per month on average. However, these are group averages—some people lose more, some less. Your GP or prescriber will discuss expected outcomes based on your individual circumstances.
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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
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Why the Difference? Mechanism and Individual Factors
The key difference lies in their mechanisms. Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways simultaneously to reduce appetite and regulate appetite signals. Wegovy is a GLP-1 receptor agonist only, activating a single pathway. This dual mechanism may explain Mounjaro's stronger average results, though the difference isn't equally pronounced for everyone.
Individual weight loss depends on many factors: your starting weight, adherence to dietary changes, physical activity levels, age, metabolism, and how your body responds to the medication. Some people see faster results with Wegovy; others respond better to Mounjaro. Use our free GLP-1 weight loss calculator above to estimate potential weight loss at different doses for context, and discuss your personal circumstances with your GP or prescriber, who can assess which medication is more suitable for you.
- 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 always better than Wegovy for weight loss?
Clinical trials show Mounjaro achieves higher average weight loss, but "better" depends on your individual circumstances. Some people respond better to Wegovy, experience fewer side effects, or find it more suitable based on other health conditions. Your prescriber will assess which is appropriate for you personally.
How much weight might I lose per month on Mounjaro?
Average monthly weight loss on Mounjaro at higher doses is approximately 1.5–2 kg, based on SURMOUNT trial data. However, this is an average—individual results vary significantly depending on starting weight, diet, activity, and personal metabolism. Your prescriber can discuss more realistic expectations.
Can I switch from Mounjaro to Wegovy if I'm not seeing results?
Possibly, but any change between medications must be managed by your prescriber. There's no official conversion chart between the two, so your prescriber would need to reassess your dose and monitor your response carefully. Discuss concerns about progress with your GP or clinic.
Which weekly weight loss injection is available on the NHS in the UK?
Both Mounjaro and Wegovy are available via NHS specialist tier 3 weight management services, subject to regional availability and individual eligibility. Access varies significantly by area, and waiting lists can be lengthy. Private online prescribing is also available.
Are the trial results realistic for real-world weight loss?
SURMOUNT and STEP trial participants followed structured diet and exercise programmes alongside medication. Real-world results can vary—some people lose similar amounts, others less. Your effort with diet and physical activity significantly influences actual weight loss. Track your progress using our free progress tracker.
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.