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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What Is 0.5mg Wegovy Equivalent to in Mounjaro?
Wegovy (semaglutide) and Mounjaro (tirzepatide) are two different prescription weight management injections licensed in the UK. A Wegovy dose of 0.5mg is approximately equivalent to a Mounjaro dose of around 2.5mg to 5mg, though there is no official conversion chart and any switch between medications must be managed by your prescriber. Both medications work differently — understanding how they compare helps you discuss options with your GP or healthcare professional.
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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.
How Wegovy and Mounjaro Differ in Mechanism and Dosing
Wegovy (semaglutide) is a GLP-1 receptor agonist that activates a single hormone pathway in the gut and brain to reduce appetite and support feeling fuller. Its dosing starts at 0.25mg and escalates gradually to a maximum of 2.4mg once weekly. Mounjaro (tirzepatide) uses a dual GIP and GLP-1 mechanism — activating two hormone pathways simultaneously — and ranges from 2.5mg to 15mg once weekly. Because Mounjaro's dual action is more potent than Wegovy's single action, lower Mounjaro doses can produce similar effects to higher Wegovy doses. The approximate equivalence is: Wegovy 0.5mg ≈ Mounjaro 2.5–5mg. However, clinical trials (STEP for Wegovy and SURMOUNT for Mounjaro) used different study designs, making direct outcome comparisons difficult. Weight loss results vary significantly between individuals regardless of which medication is used.
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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.
Prescriber Choice and Individual Suitability
Neither medication is inherently "better" — suitability depends on your individual health profile, how your body responds, and your prescriber's clinical judgment. Your GP or licensed prescriber will assess factors like your BMI, weight-related health conditions, medical history, and any other medications you take before recommending either tirzepatide or semaglutide. Use our free GLP-1 weight loss calculator to explore potential weight loss scenarios at different dose levels, and our BMI calculator to understand your current health context. Any switch from Wegovy to Mounjaro (or vice versa) must be managed by your prescriber — never change doses or switch medications without clinical guidance.
- 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.
Is 0.5mg Wegovy the same strength as 2.5mg Mounjaro?
No, they are not identical because the medications work differently. Wegovy 0.5mg is a GLP-1 only medication, whilst Mounjaro's dual GIP+GLP-1 mechanism makes it more potent. 0.5mg Wegovy is roughly equivalent to Mounjaro 2.5–5mg in effect, but individual response varies. A prescriber must assess which is suitable for you.
Can I switch from Wegovy to Mounjaro at equivalent doses?
You should never self-switch between medications. If you and your prescriber decide to switch, they will assess the appropriate Mounjaro starting dose for you — typically starting lower and titrating upwards. The approximate equivalences are a guide only, not a medical instruction.
Which medication causes more weight loss, Wegovy or Mounjaro?
Clinical trials showed Mounjaro produced slightly higher average weight loss (approximately 20.9% at maximum dose) compared to Wegovy (approximately 14.9%), but individual results vary significantly. The "best" medication depends on your personal response and health profile, not trial averages.
Do Wegovy and Mounjaro have different side effects?
Both cause similar common side effects: nausea, diarrhoea, vomiting, and constipation. These typically improve over time. Serious side effects are rare but require urgent medical attention. Your prescriber will discuss side effect profiles when assessing which medication suits you.
How do I know whether to ask for Wegovy or Mounjaro?
You don't need to choose — your GP or licensed prescriber will recommend the most appropriate medication based on your health, eligibility, and individual circumstances. Both are prescription-only and require a clinical assessment before being prescribed.
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.