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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10 ml Mounjaro vs Wegovy: How They Compare
Mounjaro and Wegovy are both prescription-only weight loss injections licensed in the UK, but they work differently and may suit different people. This guide compares both medications factually, using trial data from the SURMOUNT and STEP clinical studies. Whether you're considering either option, understanding the key differences—including mechanism, dosing, and how they're prescribed—helps you make an informed decision with your GP or prescriber. Both require a clinical assessment before prescription.
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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.
Mechanism, Dosing, and Trial Results
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways rather than one. This dual action may help regulate appetite and fat utilisation more broadly. Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single pathway. In the SURMOUNT-1 trial, Mounjaro at 10 mg produced average weight loss of approximately 19.5% of body weight over 72 weeks. In the STEP-1 trial, Wegovy at its maximum dose (2.4 mg) produced average weight loss of approximately 14.9% over 68 weeks. Both results were achieved alongside a reduced-calorie diet and increased physical activity. Mounjaro starts at 2.5 mg weekly and escalates every 4 weeks to a maximum of 15 mg. Wegovy starts at 0.25 mg and escalates over 16 weeks to a maximum of 2.4 mg. Individual results vary significantly.
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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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Eligibility and How to Access
Both Mounjaro and Wegovy are available in the UK to adults with a BMI of 30 kg/m² or above, or BMI 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Use our free BMI calculator above to check your personal BMI. Access is through NHS specialist tier 3 weight management services (with regional variation and waiting lists) or private online prescribing following a clinical assessment. A prescriber will assess your medical history, current medications, and suitability for either medication. Neither is suitable if you're pregnant, breastfeeding, or under 18. Your prescriber will recommend the medication most appropriate for your 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.
What's the main difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) activates both GIP and GLP-1 hormone pathways, whilst Wegovy (semaglutide) activates GLP-1 only. This dual mechanism in Mounjaro may account for its slightly higher average weight loss in clinical trials, but individual results vary considerably. Both work alongside diet and exercise.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching between medications is possible but must be managed by your prescriber. There is no official conversion chart between Mounjaro and Wegovy doses. Your prescriber will assess whether a switch is appropriate and guide you through the process safely, potentially starting at a lower dose.
Which is available on the NHS?
Both Mounjaro and Wegovy are approved for NHS use, but access varies significantly by region and ICB. Both are typically prescribed through specialist tier 3 weight management services following GP referral. Waiting lists can be long in many areas. Private prescribing offers faster access without NHS referral.
Are there significant differences in side effects?
Both commonly cause nausea, diarrhoea, constipation, and stomach discomfort, particularly during dose escalation. Side effect profiles are very similar. Serious side effects are rare but both require immediate medical attention if you experience severe stomach pain, gallbladder symptoms, or severe allergic reactions.
How do I decide which one to ask my prescriber about?
Your prescriber will recommend the most suitable option based on your medical history, current medications, BMI, comorbidities, and personal health goals. Neither is universally "better"—suitability is individual. Both require a clinical assessment to determine eligibility and appropriateness.
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.