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 — Which Is Best?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections licensed in the UK, but they work differently and suit different individuals. Neither is universally "best" — the right choice depends on your personal health profile, medical history, and prescriber assessment. This guide compares both medications factually so you can understand the differences and discuss options with your GP or prescriber.
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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 Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways simultaneously. This dual mechanism may help regulate appetite and support feeling fuller after meals.
Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating one hormone pathway. Both medications slow gastric emptying and work alongside a reduced-calorie diet and increased physical activity.
Clinical trial data shows average weight loss: Mounjaro approximately 15–21% body weight (SURMOUNT trial), Wegovy approximately 15% body weight (STEP trial). Individual results vary significantly. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses, though remember these are averages and your own results may differ.
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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.
Doses, Side Effects, and Eligibility
Doses: Mounjaro starts at 2.5 mg weekly, up to 15 mg maximum. Wegovy starts at 0.25 mg weekly, up to 2.4 mg maximum. Both require gradual dose titration over weeks.
Side effects: Both commonly cause nausea, diarrhoea, vomiting, and constipation — typically lessening over time. Serious side effects are rare but require immediate GP attention.
Eligibility: Both require BMI ≥30 or BMI 27–29.9 with weight-related health conditions. Prescribers assess suitability based on your individual health profile, medical history, and other medications. Neither is "better" — prescriber choice depends on your personal 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.
Is Mounjaro more effective than Wegovy?
Clinical trials show Mounjaro may produce slightly higher average weight loss (15–21% vs ~15%), but individual results vary widely. Many people achieve excellent results on either medication. Effectiveness depends on lifestyle changes, adherence, dose, and individual response — not the medication alone.
Why do prescribers choose one over the other?
Prescribers consider medical history, other medications, side effect tolerance, injection frequency preference, cost, and NHS availability. Some patients respond better to one mechanism than the other. There is no universal "best choice" — it's personalised to you.
Can I switch from Wegovy to Mounjaro?
Yes, switching is possible under prescriber guidance. Approximate dose equivalence exists (0.5 mg Wegovy ≈ 5 mg Mounjaro), but any switch must be managed by your prescriber. Do not self-switch.
Are both available on the NHS in the UK?
Both are NICE-approved, but NHS access is through specialist tier 3/4 weight management services. Availability varies significantly by region and waiting lists can be lengthy. Private access is faster through licensed UK prescribers.
What's the difference between Wegovy and Ozempic?
Both contain semaglutide, but Ozempic is licensed for type 2 diabetes (up to 2 mg), not weight loss. Wegovy is the licensed weight management version (up to 2.4 mg). Using Ozempic for weight loss is off-label in the UK.
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.