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 Benefits vs Wegovy: What's the Difference?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections available in the UK, but they work differently and offer distinct benefits. Understanding how each medication functions, the clinical trial results, and which might suit your individual circumstances can help you and your GP make an informed decision. This guide compares both options factually, without claiming one is superior to the other.
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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 — Clinical Trial Benefits
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways simultaneously. In the SURMOUNT-1 clinical trial, participants on Mounjaro 15mg achieved average weight loss of approximately 20.9% of body weight over 72 weeks alongside reduced-calorie diet and exercise.
Wegovy (semaglutide) is a GLP-1 receptor agonist only, working through a single hormone pathway. In the STEP-1 clinical trial, participants on Wegovy 2.4mg achieved average weight loss of approximately 14.9% of body weight over 68 weeks with similar lifestyle support.
These trial results represent averages — individual results vary significantly. Both medications slow gastric emptying and reduce appetite, but Mounjaro's dual mechanism may provide additional metabolic benefits, though this requires prescriber assessment for suitability.
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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.
Dosing, Eligibility, and Individual Suitability
Mounjaro escalates from 2.5mg to a maximum of 15mg weekly, while Wegovy escalates from 0.25mg to a maximum of 2.4mg weekly. Both are once-weekly injections in the form of a KwikPen device. Eligibility for both requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, hypertension, or cardiovascular disease. South Asian, Chinese, Black African, and Black Caribbean adults may qualify at lower BMI thresholds due to higher metabolic risk. Your prescriber will assess which medication — if either — suits your individual health profile, medications, and medical history. Neither medication assures specific weight loss outcomes.
- 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 medication causes less nausea — Mounjaro or Wegovy?
Both can cause nausea, particularly in the first few weeks of treatment or after dose increases. Nausea typically improves over time as your body adjusts. Individual tolerance varies widely. Your prescriber can advise on managing side effects or adjusting your dose schedule if needed.
Is Mounjaro available on the NHS in the UK?
Yes, NICE has approved tirzepatide (Mounjaro) for NHS specialist weight management services. However, NHS access varies significantly by region and often involves waiting lists. Private prescription is available through UK-licensed prescribers following online clinical assessment.
Can I switch from Wegovy to Mounjaro if Wegovy isn't working?
Potentially, yes — but any medication change must be managed by your prescriber. There is no official conversion chart between Mounjaro and Wegovy doses; your prescriber will reassess and recommend appropriate dosing based on your individual response and health.
How quickly will I see weight loss benefits with Mounjaro or Wegovy?
Weight loss typically begins within the first 4 weeks but is gradual. Most significant weight loss occurs between weeks 8 and 20 of treatment. Clinical trials showed the largest changes occurred between months 2 and 6. Patience and consistent lifestyle changes alongside medication are important.
Do I need to use both Mounjaro and Wegovy together?
No. These are alternative medications, not used together. Your prescriber will assess which single medication — if any — is appropriate for you based on your health, eligibility, and individual circumstances. Using both simultaneously is not recommended.
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.