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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Is Mounjaro the Same as Wegovy?
No, Mounjaro and Wegovy are not the same, although both are prescription-only weight loss injections licensed in the UK. The main difference is their mechanism: Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) is a GLP-1 receptor agonist only. This means Mounjaro activates two hormone pathways, whereas Wegovy activates one. Both can support weight loss alongside diet and exercise, but they work slightly differently and have different dose ranges, side effects, and clinical trial results. Your GP or prescriber will assess which is suitable for you individually.
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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 Differ
Mechanism of action: Mounjaro activates two natural hormone pathways (GIP and GLP-1), which may help regulate appetite and support feeling fuller after meals. Wegovy activates only the GLP-1 pathway. This dual action may contribute to different weight loss outcomes between the two.
Dose ranges: Mounjaro starts at 2.5 mg and escalates up to a maximum of 15 mg once weekly. Wegovy starts at 0.25 mg and escalates to a maximum of 2.4 mg once weekly. Both follow a gradual dose titration schedule over several months.
Clinical trial results: In the SURMOUNT-1 trial, Mounjaro users lost an average of 15–21% of body weight at different doses. In the STEP-1 trial, Wegovy users lost approximately 14.9% of body weight. Individual results vary significantly, and both medications are most effective when combined with a reduced-calorie diet and increased physical activity.
Side effects: Both medications can cause nausea, diarrhoea, constipation, and stomach pain, particularly during dose escalation. However, the frequency and severity may differ between individuals and between the two medications.
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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.
NHS Access and Eligibility in the UK
Both Mounjaro and Wegovy are licensed in the UK and available through NHS specialist weight management services (tier 3) and privately. NHS eligibility: Adults with a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with weight-related health conditions (such as type 2 diabetes, hypertension, or sleep apnoea) may qualify. For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds apply. Access through the NHS requires referral to a specialist tier 3 service, which varies significantly by region and can involve lengthy waiting lists.
Private access: Both medications are available privately through GPhC-registered pharmacies following an online clinical assessment with a UK-licensed prescriber. Private routes typically offer faster access but require payment. Use our GLP-1 weight loss calculator to explore potential outcomes, and our BMI calculator to check your current eligibility bracket.
- 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.
Can I switch from Mounjaro to Wegovy on the NHS?
Switching between medications requires your prescriber's assessment. There is no official conversion chart between Mounjaro and Wegovy doses. Any switch must be managed carefully by your specialist weight management team. Some NHS services may have preferred medicines, so availability varies by region.
Which is more effective — Mounjaro or Wegovy?
Clinical trials suggest Mounjaro may achieve slightly higher average weight loss (up to 21% vs 14.9% for Wegovy), but individual results vary significantly. Effectiveness depends on your personal response, adherence, diet, and exercise. Your prescriber will assess which is more appropriate for your circumstances.
Are Mounjaro and Wegovy available on the NHS?
Both are licensed in the UK and can be prescribed through NHS specialist weight management (tier 3) services. However, access varies significantly by region — some areas have limited availability or long waiting lists. NICE has approved tirzepatide (Mounjaro) for use within NHS services, but actual access depends on your local integrated care board.
Do Mounjaro and Wegovy have the same side effects?
Both commonly cause nausea, diarrhoea, constipation, and stomach pain, especially during dose escalation. Side effects typically reduce over time. However, frequency and severity may differ between individuals and between the two medications. Your prescriber can discuss potential side effects based on your health profile.
How long does it take to see weight loss results with Mounjaro or Wegovy?
Weight loss typically begins within the first few weeks, but most significant loss occurs over 12–20 weeks as doses increase. Peak results are usually seen at higher maintenance doses. Results depend on your calorie deficit, physical activity, and individual response. Both work best alongside a reduced-calorie diet and increased exercise.
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.