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 Results Before And After — How It Compares To Wegovy
When considering Mounjaro or Wegovy for weight management, understanding how the results compare can help you and your GP make an informed decision. Both are prescription-only GLP-1 receptor agonist medications licensed in the UK, but they work slightly differently and clinical trial results differ. This guide explains the evidence behind both medications, what the clinical data shows about weight loss outcomes, and how individual results vary. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses.
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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 Results — SURMOUNT vs STEP Data
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways, which distinguishes it from Wegovy's single mechanism. The SURMOUNT-1 clinical trial measured weight loss over 72 weeks at maximum maintenance doses:
- Mounjaro 5 mg: Average weight loss of approximately 15% of body weight
- Mounjaro 10 mg: Average weight loss of approximately 19.5% of body weight
- Mounjaro 15 mg: Average weight loss of approximately 20.9% of body weight
Wegovy (semaglutide) is a single GLP-1 agonist. The STEP-1 clinical trial showed average weight loss of approximately 14.9% of body weight on the maximum dose of 2.4 mg over 68 weeks. Both medications were used alongside reduced-calorie diets and increased physical activity. Individual results vary significantly, and neither medication assures specific weight loss outcomes. Your UK prescriber will discuss realistic expectations based on clinical evidence.
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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.
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Why Results Differ — Mechanism and Individual Factors
The difference in average results between Mounjaro and Wegovy reflects their different mechanisms. Mounjaro's dual GIP and GLP-1 activation may produce slightly stronger appetite suppression in some people. However, clinical trial averages mask significant individual variation — some people respond better to one medication than another, regardless of mechanism. Factors affecting results include baseline weight, age, genetics, adherence to dose escalation schedules, diet consistency, physical activity levels, and individual metabolic differences. Your GP or prescriber will assess which medication suits your health profile. Both require a UK prescription following clinical assessment and are typically available through NHS specialist weight management services or private online prescribing services. Neither medication is a standalone solution — sustainable results depend on combining medication with lifestyle changes.
- 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.
Can I switch from Mounjaro to Wegovy if I don't get results?
Yes, switching between medications is possible and managed by your prescriber. There is no official established conversion chart between Mounjaro and Wegovy doses, so your prescriber will reassess your suitability and recommend an appropriate starting dose. A switch typically requires a washout period. Always discuss with your GP or prescriber before changing medications.
Which gives better results — Mounjaro or Wegovy?
Clinical trials show Mounjaro slightly higher average results (20.9% vs clinically studied weight loss), but individual outcomes vary substantially. Some people respond better to Wegovy, others to Mounjaro. Results depend on mechanism fit, adherence, diet, activity, and genetics — not just the medication. Your prescriber will help determine which suits your health profile.
How long before I see results with Mounjaro or Wegovy?
Weight loss typically begins within the first 2–4 weeks as appetite reduces. More noticeable results usually appear after 8–12 weeks of consistent use at therapeutic doses. Both medications require gradual dose escalation (4 weeks minimum at each dose), so maximum results take 16–20+ weeks to achieve. Be patient — steady, sustainable loss is safer than gradual weight management.
Do results continue if I stop Mounjaro or Wegovy?
Weight loss results are typically not sustained if you stop the medication without maintaining dietary and lifestyle changes. Clinical trials show weight regain occurs after stopping, which is why these medications work best as part of a long-term lifestyle approach. Discuss your long-term plan with your prescriber — some people use them short-term, others longer-term.
Will my GP prescribe Mounjaro or Wegovy on the NHS?
Both medications are available through NHS specialist tier 3 weight management services, but access varies significantly by region. Waiting lists can be lengthy. Alternatively, both are available through private online prescribing services following a clinical assessment. Eligibility requires a BMI of 30+ (or 27+ with weight-related health conditions) and clinical suitability assessment.
Ready to take control of your weight loss journey?
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