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 — Complete Comparison for UK Ordering
If you're considering ordering Mounjaro or Wegovy in the UK, understanding the differences between these two prescription weight loss injections is essential. Both are licensed for weight management in UK adults, but they work through different mechanisms and have distinct dosing schedules. This guide compares the clinical evidence, eligibility criteria, and practical factors to help you and your prescriber decide which might be more suitable for your individual needs. Both require a prescription following a clinical assessment.
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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 Work — Key Differences
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two separate hormone pathways simultaneously. This dual mechanism may offer a stronger signal to your brain that you are full, potentially supporting greater appetite suppression.
Wegovy (semaglutide) is a GLP-1 receptor agonist only — it activates one hormone pathway. Both medications slow gastric emptying and reduce food cravings, but Mounjaro's dual action is the key structural difference.
Clinical trial data: In the SURMOUNT-1 trial, Mounjaro at 15 mg achieved average weight loss of approximately 20.9% of body weight over 72 weeks. In the STEP-1 trial, Wegovy at 2.4 mg achieved average weight loss of approximately 14.9% of body weight over 68 weeks. However, individual results vary significantly — some people respond well to either medication.
Our GLP-1 weight loss calculator can help you explore potential weight loss projections at different doses of either medication, based on your starting weight.
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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
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Doses, Eligibility, and How to Order in the UK
Mounjaro dosing: Starts at 2.5 mg once weekly, escalating every 4 weeks up to a maximum of 15 mg. Available as a KwikPen (4 doses per pen).
Wegovy dosing: Starts at 0.25 mg once weekly, escalating over 16 weeks to a maximum of 2.4 mg. Also a once-weekly injection.
UK eligibility (both medications): Adults with BMI ≥30, or BMI 27–29.9 with weight-related health conditions (type 2 diabetes, high blood pressure, sleep apnoea, cardiovascular disease). Lower thresholds apply for South Asian, Black African, Black Caribbean, and Chinese adults.
How to order: Both require a UK prescription from a licensed prescriber following a clinical assessment. Available through NHS specialist weight management services or private online prescribing. Your prescriber will assess which medication is most appropriate based on your individual health profile, previous treatment responses, and preferences.
- 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.
Can I switch from Wegovy to Mounjaro?
Yes, switching is possible and should be managed by your prescriber. There is no official conversion chart, but approximate equivalence suggests Wegovy 2.4 mg is roughly comparable to Mounjaro 10–15 mg. Any switch requires a new prescription and clinical assessment. Your prescriber will advise on timing and any overlap period.
Which causes fewer side effects — Mounjaro or Wegovy?
Both share similar common side effects: nausea, diarrhoea, vomiting, constipation, and stomach pain. Individual tolerance varies — some people tolerate one better than the other. Side effects typically improve after the first few weeks. Your prescriber can discuss which medication might suit your tolerance profile.
Is Mounjaro available on the NHS?
NICE has approved tirzepatide (Mounjaro) for use within NHS specialist weight management services. However, NHS availability varies significantly by region and waiting lists can be lengthy. Private prescribing access is available without NHS referral through online clinical assessments.
How long does it take to see weight loss results with Mounjaro or Wegovy?
Weight loss typically begins within 2–4 weeks of starting, though it varies between individuals. Most significant loss occurs between weeks 8–24. Both medications work best alongside reduced-calorie diet and increased physical activity. Use our free progress tracker to monitor your results over time.
What's the main advantage of Mounjaro over Wegovy?
Mounjaro's dual GIP+GLP-1 mechanism may produce greater average weight loss in clinical trials. However, this does not assures better results for you individually. Some people respond equally well or better to Wegovy. Your prescriber will recommend the most suitable option based on your health history and goals.
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.