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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Wegovy Treatment vs Mounjaro: Key Differences
Both Wegovy (semaglutide) and Mounjaro (tirzepatide) are prescription-only weight loss injections licensed in the UK for adults with obesity or overweight with health conditions. While they work through similar pathways—both are GLP-1 receptor agonists or dual agonists—they differ in mechanism, dose escalation, and clinical trial outcomes. Understanding these differences helps you and your GP decide which treatment may be most suitable for your individual circumstances. This guide compares the two evidence-based options available in the UK today. Use our free GLP-1 weight loss calculator to explore projected outcomes at different doses.
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Calculate Your BMI Instantly
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.
Mechanism, Doses, and Clinical Trial Data
Wegovy (semaglutide) is a GLP-1 receptor agonist—it activates a single hormone pathway to reduce appetite and support feeling fuller after smaller meals. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, activating two pathways simultaneously, which may offer additional effects on appetite and fat utilisation.
Dose escalation: Wegovy starts at 0.25 mg and escalates to a maximum of 2.4 mg weekly over 16+ weeks. Mounjaro starts at 2.5 mg and escalates to 15 mg weekly over 20+ weeks, offering more dose flexibility.
Clinical trial outcomes: In the STEP-1 trial, Wegovy helped participants lose an average of 14.9% of body weight at the maximum dose. In the SURMOUNT-1 trial, Mounjaro achieved average weight loss of 20.9% at the maximum dose—though individual results vary significantly. Both trials included reduced-calorie diet and increased physical activity.
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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 Treatment Is Right for You?
Neither Wegovy nor Mounjaro is "better"—suitability depends on your individual health profile, medical history, and how you respond to treatment. Your GP or prescriber will assess you using NHS eligibility criteria: BMI of 30 or above, or BMI of 27–29.9 with weight-related conditions like type 2 diabetes, high blood pressure, or cardiovascular disease.
Both medications require a clinical assessment before prescription. Availability through the NHS varies by region—many areas have long waiting lists for specialist tier 3 services. Private prescribing offers faster access following an online clinical assessment. Start by calculating your BMI using our free BMI calculator, then discuss your options with your GP or a licensed UK prescriber. Both require ongoing monitoring and are most effective alongside 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.
What is the main difference between Wegovy and Mounjaro?
Wegovy (semaglutide) is a single GLP-1 receptor agonist. Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, activating two hormone pathways. This dual mechanism in Mounjaro may contribute to slightly higher average weight loss in clinical trials, though individual results vary.
Which medication causes fewer side effects?
Both have similar common side effects: nausea, diarrhoea, constipation, and stomach pain, especially during dose escalation. Side effect profiles are comparable. Your body's tolerance depends on individual factors. Your prescriber will monitor you and adjust doses if needed.
Can I switch from Wegovy to Mounjaro?
Yes, switching is possible and managed by your prescriber. Approximate dose equivalences exist (0.25 mg Wegovy ≈ 0.5 mg Mounjaro; 2.4 mg Wegovy ≈ 15 mg Mounjaro), but any switch requires medical supervision to ensure safe transition and appropriate monitoring.
How do I access Wegovy or Mounjaro on the NHS?
Both are available through NHS specialist tier 3 weight management services via GP referral. Access varies by region and availability can be limited with waiting lists. Private prescribing offers faster access through online clinical assessments with UK-licensed prescribers.
Do I need a clinical assessment before treatment?
Yes, both medications require a thorough clinical assessment to confirm eligibility, check for contraindications, and ensure safety. Your GP or prescriber will review your medical history, current medications, and weight-related health conditions before issuing a prescription.
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.