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 Weight Loss Injection Is Right for You?
Both Mounjaro (tirzepatide, manufactured by Eli Lilly) and Wegovy (semaglutide) are prescription weight loss injections licensed in the UK. They work differently and may suit different people. Mounjaro uses a dual GIP and GLP-1 mechanism, while Wegovy uses GLP-1 only. Both require a prescription and clinical assessment before starting. Understanding the key differences—including mechanism, dosing, clinical trial results, and individual suitability—can help you and your prescriber decide which option might be appropriate for your situation. Try our 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.
How Mounjaro and Wegovy Work — Clinical Trial Results and Mechanism
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways to help regulate appetite and blood sugar. In the SURMOUNT-1 clinical trial, participants on the maximum 15 mg dose lost an average of 20.9% of their body weight over 72 weeks, alongside diet and exercise changes.
Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating one hormone pathway. In the STEP-1 trial, participants on 2.4 mg lost an average of 14.9% of body weight over 68 weeks. The dual mechanism of Mounjaro may account for the slightly higher average weight loss in trials, though individual results vary significantly and cannot be assured.
- Mounjaro: 2.5 mg to 15 mg, once weekly via KwikPen
- Wegovy: 0.25 mg to 2.4 mg, once weekly via pre-filled pen
- Both require minimum 4 weeks at each dose before increasing
- Both are used alongside reduced-calorie diet and physical activity
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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.
Choosing Between Mounjaro and Wegovy — What Your Prescriber Will Consider
Both medications require a prescription and clinical assessment—your GP or specialist will assess which is more suitable based on your health history, current medications, and individual circumstances. There is no official conversion between Mounjaro and Wegovy, though approximate equivalences exist (e.g. Mounjaro 10 mg is roughly equivalent to Wegovy 1.7 mg). Side effects are similar between both—nausea, diarrhoea, and constipation are common early on and often improve with time.
In the UK, access is available through NHS specialist tier 3 weight management services (which may have waiting lists) or private online prescribing following a remote consultation. Use our BMI calculator to check your starting point, and our weight converter to track progress in stone or kg—whichever you prefer.
- 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 suggest Mounjaro may lead to slightly higher average weight loss (20.9% vs 14.9%), but this reflects trial averages only. Individual results vary significantly. Some people respond better to one medication than the other. Effectiveness depends on your genetics, lifestyle adherence, and how your body responds—only a prescriber can assess which suits you.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching is possible but must be managed by your prescriber. There is no official established conversion chart. Your prescriber will assess whether a switch is appropriate and guide the transition. Do not stop one and start another without medical supervision.
What's the difference between Mounjaro and Ozempic?
Both contain semaglutide but are different formulations. Ozempic is licensed for type 2 diabetes (up to 2 mg). Mounjaro is tirzepatide, a different medication. Mounjaro uses a dual GIP+GLP-1 mechanism, whereas Ozempic is GLP-1 only. They are not interchangeable.
How do I access Mounjaro or Wegovy in the UK?
NHS access is through specialist tier 3 weight management services via GP referral (availability and waiting times vary by region). Private access is through UK-licensed prescribers via online consultation with GPhC-registered pharmacies. Both require clinical assessment and a prescription—neither is available over the counter.
Which weight loss injection is available on the NHS?
Both Mounjaro and Wegovy are approved by NICE for NHS use, but access depends on your ICB (Integrated Care Board) and whether you meet local eligibility criteria. Some areas may have limited availability or long waiting lists. Your GP can advise on NHS options in your area and whether private access may be faster.
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.