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 Last Dose vs Wegovy: What's the Difference?
If you're considering GLP-1 weight loss injections in the UK, you've likely heard both Mounjaro and Wegovy mentioned. Both are prescription-only medications, but they work differently and reach their maximum doses at different points. Understanding how they compare — from their last dose upwards — helps you and your GP or prescriber make an informed decision about which may be suitable for you. Individual results vary, and both require clinical assessment before prescription.
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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.
How Mounjaro and Wegovy Differ at Maximum Dose
Mounjaro (tirzepatide) reaches its maximum dose of 15 mg once weekly after approximately 20 weeks of dose titration. It is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways simultaneously. In the SURMOUNT-1 clinical trial, participants on the maximum 15 mg dose lost an average of 20.9% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) reaches its maximum dose of 2.4 mg once weekly after approximately 16 weeks of dose escalation. It is a GLP-1 receptor agonist only, activating a single hormone pathway. In the STEP-1 clinical trial, participants on 2.4 mg lost an average of 14.9% of their body weight over 68 weeks, with the same lifestyle support.
- Mounjaro: dual mechanism may support greater average weight loss
- Wegovy: single mechanism, well-established track record
- Both are once-weekly injections administered as pre-filled pens
- Both require prescription and clinical assessment
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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 Is Right for You? Individual Suitability Matters
Trial averages do not predict individual outcomes — your prescriber will assess which medication suits your circumstances based on your health history, other medications, and personal needs. Neither Mounjaro nor Wegovy is inherently "better"; they are different tools for different people. Some patients may tolerate one better than the other, or respond more effectively to one mechanism over another. Your GP or specialist can discuss the pros and cons of each, including gastrointestinal side effects, injection technique, and cost. Use our free GLP-1 weight loss calculator to explore projected weight loss at different doses, and our BMI calculator to understand your starting point. Both medications work best alongside sustained dietary changes and increased physical activity.
- 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's the main difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP and GLP-1 agonist (15 mg max), while Wegovy is a GLP-1 agonist only (2.4 mg max). The SURMOUNT trial showed Mounjaro users lost an average of 20.9% body weight; STEP trials showed Wegovy users lost approximately 14.9%. Both require prescription and clinical assessment.
How long does it take to reach the last dose with each medication?
Mounjaro takes approximately 20 weeks to reach the maximum 15 mg dose, escalating every 4 weeks starting from 2.5 mg. Wegovy takes approximately 16 weeks to reach 2.4 mg, escalating every week starting from 0.25 mg. Your prescriber may adjust timings based on side effects.
Are Mounjaro and Wegovy available on the NHS in the UK?
Both are available through NHS specialist weight management services (tier 3), though regional availability and waiting lists vary significantly. They are also available privately through UK-licensed prescribers following an online clinical assessment.
Can I switch from Wegovy to Mounjaro or vice versa?
Yes, switching is possible but must be managed by your prescriber. There is no official conversion chart — approximate equivalences exist (e.g., Wegovy 2.4 mg ≈ Mounjaro 15 mg), but any transition requires medical guidance to avoid gaps or overlaps.
How do I know which medication to ask my GP about?
Discuss your medical history, weight loss goals, and any previous medication experience with your GP or specialist. They will assess your eligibility and suitability based on your BMI, health conditions, and individual circumstances. Both require a prescription and cannot be purchased without 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.