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 to Order in the UK
If you're considering a weight loss injection in the UK, you've likely heard of both Mounjaro and Wegovy. Both are prescription-only GLP-1 medications licensed for weight management, but they work differently and have different dose schedules. This guide compares the two side-by-side so you can understand the key differences before speaking to a prescriber about which might suit 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.
Clinical Trial Data and How They Work
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways in your body. In the SURMOUNT-1 clinical trial over 72 weeks, participants taking Mounjaro 15 mg lost an average of 20.9% of their body weight alongside reduced-calorie diet and increased physical activity. At the 10 mg dose, average loss was 19.5%.
Wegovy (semaglutide) is a GLP-1-only receptor agonist, activating a single hormone pathway. In the STEP-1 clinical trial over 68 weeks, participants taking Wegovy 2.4 mg lost an average of 14.9% of body weight under the same lifestyle conditions.
- Mounjaro: dual mechanism (GIP + GLP-1), maximum dose 15 mg once weekly
- Wegovy: single mechanism (GLP-1 only), maximum dose 2.4 mg once weekly
- Both require reduced-calorie diet and physical activity for optimal results
- Individual results vary significantly between 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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Dose Schedules and How to Order in the UK
Dose escalation differs between the two. Mounjaro starts at 2.5 mg and increases every 4 weeks up to a maximum of 15 mg. Wegovy starts at 0.25 mg and increases weekly up to 2.4 mg. Both are once-weekly injections available as pre-filled pens.
To order either medication in the UK, you have two main routes: NHS specialist weight management services (typically through GP referral to tier 3 services, though waiting lists vary) or private online prescribing through a UK-licensed prescriber. Your prescriber will assess your BMI, health conditions, and medical history before issuing a prescription. Use our GLP-1 weight loss calculator above to explore estimated outcomes at different doses.
Dose escalation differs between the two. Mounjaro starts at 2.5 mg and increases every 4 weeks up to a maximum of 15 mg. Wegovy starts at 0.25 mg and increases weekly up to 2.4 mg. Both are once-weekly injections available as pre-filled pens.
To order either medication in the UK, you have two main routes: NHS specialist weight management services (typically through GP referral to tier 3 services, though waiting lists vary) or private online prescribing through a UK-licensed prescriber. Your prescriber will assess your BMI, health conditions, and medical history before issuing a prescription. Use our GLP-1 weight loss calculator above to explore estimated 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.
Which weight loss injection is better, Mounjaro or Wegovy?
Neither is objectively "better" — suitability depends on your individual health profile, medical history, and how your body responds. Clinical trials show Mounjaro achieved slightly higher average weight loss (20.9% vs 14.9%), but individual results vary significantly. A prescriber will assess which is more appropriate for you during a clinical consultation.
Can I switch from Wegovy to Mounjaro or vice versa?
Yes, switching is possible, but it must be managed by your prescriber. There is no official established conversion chart between the two. Your prescriber will assess whether a switch is clinically appropriate and will manage the transition carefully to avoid side effects.
How do I order Mounjaro or Wegovy online in the UK?
Both medications are available through private online prescribing. You'll complete an online health assessment with a UK-licensed prescriber. If approved, a prescription is issued and the medication is dispensed by a GPhC-registered pharmacy. Costs and availability vary by provider.
What's the difference between Mounjaro and Ozempic?
Both contain semaglutide, but Ozempic (up to 2 mg) is licensed for type 2 diabetes, not weight management. Wegovy (up to 2.4 mg) is the licensed weight management version. Using Ozempic for weight loss in the UK is off-label and not recommended.
Do both medications work with the NHS?
Both are approved by NICE and available through NHS specialist tier 3 weight management services. However, access varies significantly by region, and waiting lists can be lengthy. Private prescribing offers faster access without NHS referral.
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.