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 — How They Compare in the UK
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections licensed in the UK, but they work differently. Mounjaro is a dual GIP and GLP-1 receptor agonist, whilst Wegovy activates only the GLP-1 pathway. Understanding their differences — including dose ranges, trial results, and side effect profiles — helps you and your GP or prescriber decide which might be more suitable for your individual health. Both require a clinical assessment before prescription. Use our free GLP-1 weight loss calculator to explore potential outcomes with either medication.
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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.
Mechanism, Doses, and Trial Data Compared
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways simultaneously. This dual mechanism may provide stronger appetite suppression and blood sugar regulation. Wegovy (semaglutide) is a single GLP-1 receptor agonist, activating one pathway.
Dose ranges: Mounjaro escalates from 2.5 mg to a maximum of 15 mg once weekly. Wegovy escalates from 0.25 mg to a maximum of 2.4 mg once weekly — a much smaller absolute dose due to its different potency.
Trial outcomes: In the SURMOUNT-1 trial, Mounjaro at 15 mg achieved average weight loss of approximately 20.9% of body weight. In the STEP-1 trial, Wegovy at 2.4 mg achieved approximately 14.9% average weight loss. Both trials included participants following a reduced-calorie diet and increased physical activity. Individual results vary significantly, and clinical trial averages do not predict personal outcomes.
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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.
Eligibility, Side Effects, and Your Next Step
Both medications are eligible for UK adults with a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Lower thresholds apply for South Asian, Chinese, Black African, and Black Caribbean adults due to higher health risks at lower BMI levels.
Side effects are similar between both medications — nausea, diarrhoea, vomiting, and constipation are very common initially. The choice between them is not based on side effects alone, but on individual clinical suitability, medical history, and prescriber recommendation. Your GP or a licensed online prescriber will assess which is more appropriate for you. Calculate your BMI now using the free tool on this page to understand your starting point.
- 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 show Mounjaro achieved slightly higher average weight loss (approximately 20.9% vs 14.9%), but this does not mean it will work better for every individual. Results depend on metabolism, adherence, diet, activity, and other health factors. Prescriber guidance is essential for choosing the right medication for your circumstances.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching between medications requires prescriber oversight. Mounjaro is not a direct replacement dose for Wegovy — approximate equivalences exist (e.g., Wegovy 2.4 mg ≈ Mounjaro 10–15 mg), but any switch must be managed by your prescriber with proper monitoring.
How much does each cost on the NHS in the UK?
Both Mounjaro and Wegovy are available through NHS specialist tier 3 weight management services, though access and availability vary significantly by region and waiting times can be lengthy. Private costs range from approximately £129–£320 per month depending on dose and provider.
Which one is better for type 2 diabetes?
Both improve blood sugar control, but Mounjaro's dual mechanism may offer additional benefit for diabetes management. However, suitability depends on individual health history. Always discuss with your GP or prescriber, as some diabetes medications may need adjustment alongside weight loss therapy.
How long does it take to see results with either medication?
Weight loss typically begins within the first few weeks as doses are escalated. Most significant results appear after 8–12 weeks of treatment at therapeutic doses. Full clinical trial periods lasted 68–72 weeks. Consistent diet and physical activity are essential alongside medication for best results.
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.