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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Mounjaro vs Wegovy โ What the UK Clinical Data Shows
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections licensed in the UK, but they work differently and produce different results in clinical trials. You'll often see "success stories" shared online, but the reality is more nuanced โ individual results vary significantly, and both medications work best alongside diet and exercise. This guide compares the clinical evidence from the SURMOUNT and STEP trials, explains how they differ, and clarifies what "success" actually means for each medication. Your GP or prescriber will assess which option is suitable for your personal health circumstances.
10,000+ calculations today ยท NHS-aligned thresholds ยท 100% free
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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/mยฒ).
While BMI isn't a perfect measure โ it doesn't account for muscle mass, bone density, or fat distribution โ 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 โ 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 Results โ SURMOUNT vs STEP
The most reliable way to compare Mounjaro and Wegovy is through their clinical trials, which tested real-world effectiveness:
- Mounjaro (SURMOUNT-1 trial): At the maximum 15 mg dose, participants lost an average of 20.9% of their body weight over 72 weeks. At 10 mg, average loss was 19.5%. These results combined medication with reduced-calorie diet and increased physical activity.
- Wegovy (STEP-1 trial): At the maximum 2.4 mg dose, participants lost an average of 14.9% of their body weight over 68 weeks, also alongside lifestyle changes.
The key difference: Mounjaro's dual GIP and GLP-1 mechanism appears to produce slightly greater average weight loss than Wegovy's single GLP-1 mechanism. However, individual results vary considerably โ some people lose more on Wegovy, others respond better to Mounjaro. Your prescriber will consider your personal health profile when deciding which is more suitable.
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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 โ 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 โ completely free.
How They Work Differently โ Mechanism Matters
The "success" you see in online reviews often depends on understanding how these medications differ mechanically:
- Mounjaro (tirzepatide): Activates both GIP and GLP-1 hormone pathways โ dual action that may amplify appetite suppression and improve how your body processes fat.
- Wegovy (semaglutide): Activates GLP-1 only โ proven, effective single-pathway approach that has been used in clinical practice for several years.
Neither is inherently "better" โ which works better for you depends on your individual metabolism, side effect tolerance, and health conditions. A licensed prescriber will assess whether Mounjaro's KwikPen, Wegovy's pen, dose titration schedule, or cost fits your circumstances. Use our GLP-1 weight loss calculator to estimate potential results at different doses, then discuss with your GP or prescriber which medication aligns with your goals.
- 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 โ 5mg โ 7.5mg โ 10mg โ 12.5mg โ 15mg
- GLP-1 receptor agonist
- Up to 15โ17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg โ 0.5mg โ 1mg โ 1.7mg โ 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 | 15โ22.5% | 12โ17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20โ32 weeks | 16โ20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | ยฃ150โยฃ250/month | ยฃ150โยฃ300/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 โ 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.
Do the "success stories" you see online apply to me?
Online success stories are real for those individuals, but they don't predict your personal outcome. Clinical trials show average weight loss of 14.9โ20.9% depending on medication and dose, but results vary widely. Your age, metabolism, adherence to diet and exercise, starting weight, and existing health conditions all affect your outcome. Only a prescriber can assess your suitability.
Is Mounjaro more successful than Wegovy?
In clinical trials, Mounjaro showed slightly higher average weight loss (20.9% vs 14.9%). However, "success" is personal. Some people lose more on Wegovy. Both are prescription-only and require clinical assessment. Neither assures results โ lifestyle changes remain essential.
How long does it take to see results with these injections?
Most people notice appetite changes within 1โ2 weeks. Measurable weight loss typically appears by week 4โ6. Full results develop gradually over 12โ16 weeks as doses increase. Using our progress tracker can help you log changes week by week and stay motivated.
Are side effects different between Mounjaro and Wegovy?
Both cause similar common side effects: nausea, diarrhoea, constipation, and stomach pain โ especially during dose increases. Individual tolerance varies. Some people tolerate Mounjaro better; others prefer Wegovy. Your prescriber will manage side effects and adjust doses if needed.
How do I get either medication on the NHS in the UK?
Both require referral to a specialist tier 3 or 4 weight management service from your GP. Access varies by region. Waiting lists can be long. Alternatively, private online prescribing services (via GPhC-registered pharmacies) offer faster access following an online clinical assessment.
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.