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 vs Mounjaro: Dose Equivalence and Key Differences
Comparing Wegovy and Mounjaro doses can help you understand these two prescription weight loss injections, but the concept of direct "equivalence" is more nuanced than simple numbers. Both medications work differently — Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1 agonist only. Although approximate dose relationships exist based on clinical practice, any switch between medications must be managed by your prescriber. This guide explains the mechanisms, trial data, and how UK doctors approach dosing decisions for tirzepatide and semaglutide.
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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.
Dose Comparison and Clinical Trial Data
Approximate dose equivalence is often suggested in clinical practice, though no official conversion chart exists:
- Mounjaro 5 mg ≈ Wegovy 0.5 mg
- Mounjaro 10 mg ≈ Wegovy 1.7 mg
- Mounjaro 15 mg ≈ Wegovy 2.4 mg
However, these are rough approximations only. The medications work through different pathways — Mounjaro activates both GIP and GLP-1 receptors, whilst Wegovy activates GLP-1 alone. Clinical trial data shows similar overall weight loss outcomes: in the SURMOUNT-1 trial, Mounjaro 15 mg achieved approximately 20.9% average weight loss over 72 weeks, while the STEP-1 trial showed Wegovy 2.4 mg achieved approximately 14.9% average weight loss over 68 weeks. Results vary significantly between individuals. Any medication switch must be prescribed and monitored by your GP or specialist.
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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.
Choosing Between Mounjaro and Wegovy in the UK
Your prescriber decides which medication suits your individual health circumstances — this is not a choice you make independently. Both require a clinical assessment confirming eligibility (BMI ≥30, or ≥27 with weight-related health conditions). NHS access is through specialist tier 3 weight management services with significant regional variation. Private access is available through UK-licensed prescribers following online consultation. Factors your prescriber considers include your medical history, other medications, side effect tolerance, and previous response to GLP-1 treatment. Use our free BMI calculator to check your starting point, and our GLP-1 weight loss calculator to explore projected outcomes at different doses of either medication.
- 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 difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, activating two hormone pathways. Wegovy (semaglutide) is a GLP-1 agonist only, activating one pathway. This different mechanism may explain why some people respond better to one than the other, though clinical trial weight loss outcomes are broadly similar when used as prescribed.
Can I switch from Wegovy to Mounjaro or vice versa?
Yes, but only under prescriber guidance. There is no official conversion formula. Your GP or specialist will assess whether a switch is appropriate for you, and if so, will typically restart you on a lower dose and titrate up gradually. Never switch medications without medical supervision.
Is there an exact dose equivalent between Mounjaro and Wegovy?
No official conversion exists. Approximate relationships are used in clinical practice (e.g. Mounjaro 10 mg ≈ Wegovy 1.7 mg), but these are rough guides only. The medications' different mechanisms mean "equivalent" doses are not directly comparable. Your prescriber will determine appropriate dosing if switching.
Which weight loss injection is more effective — Mounjaro or Wegovy?
Clinical trials show similar average weight loss outcomes (~15–21% body weight), but results vary significantly between individuals. Neither is universally "more effective" — individual response depends on genetics, compliance, lifestyle changes, and personal health factors. Your prescriber will discuss suitability based on your circumstances.
How do I access Mounjaro or Wegovy in the UK?
Both are prescription-only and require clinical assessment. NHS access is through specialist weight management services (tier 3) — availability varies by region. Private access is available through UK-licensed prescribers following an online consultation with a GPhC-registered pharmacy. Your GP can advise on NHS pathways in your area.
Ready to take control of your weight loss journey?
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