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 vs Wegovy — Are They Equivalent?
Mounjaro (tirzepatide) and Wegovy (semaglutide) are both prescription-only weight management injections licensed in the UK, but they work differently. While approximate dose equivalencies exist, they are not directly interchangeable. This guide explains how they compare, what the clinical trial data shows, and how your GP or prescriber will decide which is suitable for you. Both medications work by activating appetite-regulating pathways, but the mechanism — and therefore individual response — differs between them.
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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 Compare — Mechanism and Dosing
Mechanism: Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways. Wegovy is a GLP-1 receptor agonist only, activating a single pathway. This dual action in Mounjaro may explain why some clinical trial data suggests slightly higher average weight loss, though individual results vary significantly.
Dose ranges: Mounjaro starts at 2.5 mg and escalates to a maximum of 15 mg once weekly. Wegovy starts at 0.25 mg and escalates to 2.4 mg once weekly. Both use a step-by-step titration schedule, with minimum 4 weeks on each dose before increasing.
Approximate equivalence: While not official medical conversions, clinical practice suggests: Mounjaro 5 mg ≈ Wegovy 0.5 mg; Mounjaro 10 mg ≈ Wegovy 1.7 mg; Mounjaro 15 mg ≈ Wegovy 2.4 mg. Any switch between medications must be managed by your prescriber.
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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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Clinical Trial Results and Individual Suitability
Weight loss outcomes: SURMOUNT-1 trials showed Mounjaro users lost approximately 15–21% of body weight at 72 weeks. STEP-1 trials showed Wegovy users lost approximately 15% of body weight at 68 weeks. Both figures are averages — individual results vary considerably based on diet adherence, physical activity, genetics, and other health factors.
Choosing between them: Your GP or prescriber will assess which medication is appropriate for you based on your health profile, any existing conditions, other medications, and individual suitability. UK prescription eligibility requires a BMI of 30 or above (or 27–29 with weight-related health conditions). Neither is objectively "better" — the right choice depends on your individual circumstances.
- 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 activates two hormone pathways (GIP and GLP-1), while Wegovy activates one (GLP-1 only). This dual mechanism in Mounjaro may explain modest differences in weight loss averages in clinical trials, but individual results vary significantly regardless of which medication is used.
Can I switch from Wegovy to Mounjaro?
Switching between medications is possible but must be managed by your prescriber. There is no official conversion chart — your prescriber will assess your individual response and adjust doses accordingly. Never switch medications without medical guidance.
Which one loses more weight, Mounjaro or Wegovy?
Clinical trial averages favour Mounjaro slightly (15–21% vs clinically studied weight loss), but individual results vary. Factors like diet, exercise, genetics, and medication adherence matter far more than which drug you use. Your prescriber will choose based on suitability for you, not just outcomes.
How do I get Mounjaro or Wegovy on the NHS in the UK?
Both are available through NHS specialist tier 3 weight management services by GP referral. Availability and waiting lists vary significantly by region. Private prescription access is also available through online consultations with UK-licensed prescribers.
Are Mounjaro and Wegovy the only UK weight loss injections?
No. Saxenda (liraglutide) is also licensed for UK weight management, though it is a daily injection rather than weekly. Your GP can discuss all three options and which may be suitable for your individual health circumstances.
Ready to take control of your weight loss journey?
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