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 Medication Is Right for You?
Mounjaro and Wegovy are both prescription-only weight loss injections available in the UK, but they're made by different manufacturers and work slightly differently. Mounjaro is manufactured by Eli Lilly as a tirzepatide injection, while Wegovy is made by Novo Nordisk as a semaglutide injection. Understanding the differences between these two medications can help you and your GP or prescriber decide which might be more suitable for your individual health needs. 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.
How Mounjaro and Wegovy Work: Mechanism Differences
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways in your body. This dual mechanism may help regulate appetite more effectively by working on two separate signals. In the SURMOUNT-1 clinical trial, participants taking Mounjaro at the maximum 15 mg dose lost an average of approximately 20.9% of their body weight over 72 weeks.
Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single hormone pathway. In the STEP-1 clinical trial, participants taking the maximum 2.4 mg dose lost an average of approximately 14.9% of their body weight over 68 weeks. Both medications slow how quickly food leaves your stomach and help you feel fuller after smaller meals. Try our GLP-1 weight loss calculator above to explore potential weight loss projections at different doses of either medication.
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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 NHS Access in the UK
Mounjaro starts at 2.5 mg weekly and escalates to a maximum of 15 mg, while Wegovy begins at 0.25 mg and reaches a maximum of 2.4 mg. Both cause similar common side effects including nausea, diarrhoea, vomiting, and constipation, though individual tolerability varies. On the NHS, both medications are available through specialist tier 3 weight management services, though access and waiting times vary significantly by region. Privately, both can be prescribed following an online clinical assessment. Your prescriber will assess your individual health profile, BMI, weight-related health conditions, and medication history to determine which medication is more appropriate for you.
- 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 is a dual GIP and GLP-1 receptor agonist made by Eli Lilly, while Wegovy is a GLP-1-only medication made by Novo Nordisk. This means Mounjaro activates two hormone pathways, whereas Wegovy activates one. Both are prescription-only and work to reduce appetite and support weight loss alongside diet and exercise.
Which medication causes more weight loss — Mounjaro or Wegovy?
In clinical trials, Mounjaro showed slightly higher average weight loss (approximately 20.9% at maximum dose) compared to Wegovy (approximately 14.9% at maximum dose). However, individual results vary significantly, and what works best depends on your personal response, health conditions, and prescriber guidance. Neither outcome is assured.
Can I get Mounjaro or Wegovy on the NHS in the UK?
Both medications are available on the NHS through specialist tier 3 weight management services. However, access varies by region and NHS availability is limited. Waiting lists can be lengthy in many areas. Both are also available privately through registered online prescribing services following a clinical assessment.
Are the side effects the same for Mounjaro and Wegovy?
Both medications cause similar common side effects including nausea, diarrhoea, constipation, and stomach pain, particularly when starting or increasing doses. Individual side effect profiles vary. Serious side effects are rare but can include pancreatitis. Always discuss side effect concerns with your prescriber.
How do I know which medication my GP will prescribe?
Your GP or prescriber will assess your medical history, current health conditions, weight, BMI, and other medications to determine which is most suitable. Both require a clinical assessment. You can use our free BMI calculator to check your current BMI as context before your appointment, and discuss both options with your healthcare professional.
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.