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: UK Comparison Guide
Both Wegovy (semaglutide) and Mounjaro (tirzepatide) are prescription-only weight loss injections licensed in the UK, but they work differently and may suit different people. Wegovy is a GLP-1 receptor agonist approved by NICE, while Mounjaro is a dual GIP and GLP-1 agonist — offering two hormone pathways rather than one. Understanding how they compare can help you discuss options with your GP or prescriber. This guide breaks down the key differences to help you make an informed decision about which might be right for you.
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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 Wegovy and Mounjaro Work — The Main Difference
Wegovy (semaglutide) activates GLP-1 receptors only — a single hormone pathway that signals fullness, reduces appetite, and slows how quickly food leaves your stomach. The STEP clinical trials showed Wegovy helps participants lose an average of around 15% of their body weight at the maximum 2.4 mg dose over 68 weeks, alongside a reduced-calorie diet and increased physical activity.
Mounjaro (tirzepatide) activates both GIP and GLP-1 receptors — a dual mechanism that may enhance appetite suppression and metabolic effects. The SURMOUNT clinical trials showed Mounjaro achieves average weight loss of 15% to 21% depending on dose, with the 15 mg maximum dose reaching approximately clinically studied weight loss. Both are once-weekly injections, but they use different biological pathways to support weight loss. Individual results vary significantly, and either may be more effective for particular people.
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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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Doses, Side Effects, and UK Access
Wegovy doses: Start at 0.25 mg, escalating over 16 weeks to a maximum of 2.4 mg once weekly. Mounjaro doses: Start at 2.5 mg, escalating to a maximum of 15 mg once weekly over 20 weeks. Both share similar common side effects — nausea, diarrhoea, constipation, and stomach pain — though individual tolerance varies. In the UK, both are prescription-only and available through NHS specialist weight management services (with potential waiting lists) or private prescribers following clinical assessment. Your GP or licensed prescriber will assess which is more suitable based on your health history, BMI, and any weight-related conditions. Use our free GLP-1 weight loss calculator above to explore potential outcomes at different doses.
- 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 Mounjaro more effective than Wegovy?
Clinical trials suggest Mounjaro may achieve slightly higher average weight loss (up to 21% vs 15%), but individual results vary significantly. Effectiveness depends on your personal response, lifestyle, and adherence. A prescriber can discuss which suits your specific situation.
Can you switch from Wegovy to Mounjaro in the UK?
Yes, switching is possible under prescriber guidance, though there is no official conversion chart. Approximate equivalences exist — for example, Wegovy 1.7 mg is roughly comparable to Mounjaro 10 mg — but any switch must be managed by your GP or prescriber to ensure safe transition.
What is Ozempic and how does it differ from Wegovy?
Both contain semaglutide, but Ozempic (up to 2 mg) is licensed for type 2 diabetes, not weight loss. Wegovy (up to 2.4 mg) is the licensed weight management version in the UK. Using Ozempic for weight loss is off-label and not recommended — always use the licensed medication for the intended purpose.
Are Wegovy and Mounjaro available on the NHS in the UK?
Both are approved by NICE for NHS use through specialist tier 3 weight management services, but availability, eligibility, and waiting times vary significantly by region. Your GP can refer you to your local specialist service. Private prescribing is also available following an online clinical assessment.
Which injection should I choose — Wegovy or Mounjaro?
This depends on your individual health profile, BMI, any weight-related conditions, tolerance for side effects, and prescriber assessment. Neither is universally "better" — both are effective prescription-only medications. Use our BMI calculator above to check your eligibility, then discuss both options with your GP or a licensed prescriber.
Ready to take control of your weight loss journey?
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