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
Free tracker included with every download this week
Mounjaro 15mg vs Wegovy — Which Is Right for You?
Mounjaro and Wegovy are both prescription-only weight management injections licensed in the UK, but they work differently and have different maximum doses. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist that reaches a maximum dose of 15mg once weekly, whilst Wegovy (semaglutide) is a GLP-1-only medication with a maximum dose of 2.4mg once weekly. This guide breaks down the key differences, compares clinical trial results, and explains how your prescriber decides which medication may be suitable for you. Both require a clinical assessment before prescription.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
Clinical Trial Results and Key Differences
Mechanism of action: Mounjaro activates two hormone pathways (GIP and GLP-1), whilst Wegovy activates GLP-1 only. This dual action in Mounjaro may help regulate appetite and fat utilisation more broadly.
SURMOUNT vs STEP trial data: Mounjaro clinical trials (SURMOUNT-1) showed average weight loss of approximately 15% at 5mg, 19.5% at 10mg, and 20.9% at 15mg over 72 weeks. Wegovy trials (STEP-1) showed approximately 14.9% average weight loss at the maximum dose (2.4mg) over 68 weeks. Both studies included participants following a reduced-calorie diet and increased physical activity.
Important context: These are clinical trial averages. Individual results vary significantly, and these figures do not assures specific weight loss outcomes for any individual.
Injection frequency: Both are once-weekly injections, making them equally convenient for weekly administration using a pre-filled KwikPen device.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Eligibility, Suitability, and Prescriber Assessment
Both Mounjaro and Wegovy have identical UK eligibility criteria: adults with a BMI of 30 or above, or BMI of 27–29.9 with at least one weight-related health condition such as type 2 diabetes, high blood pressure, or cardiovascular disease. Lower BMI thresholds may apply for South Asian, Chinese, Black African, or Black Caribbean adults.
Your prescriber will assess which medication is most suitable based on your individual health profile, medical history, other medications, and personal preferences. There is no blanket "better" option—both are effective, and choice depends on individual suitability. Your GP or a licensed prescriber can discuss which aligns best with 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) is a dual GIP and GLP-1 receptor agonist, whilst Wegovy (semaglutide) is GLP-1-only. Mounjaro's dual mechanism may work on appetite regulation differently. Mounjaro's maximum dose is 15mg weekly; Wegovy's is 2.4mg weekly. Both are once-weekly injections.
Which one causes more weight loss?
Clinical trials showed Mounjaro achieved slightly higher average weight loss (up to 20.9% at 15mg) compared to Wegovy (14.9% at 2.4mg). However, individual results vary significantly. Your prescriber will discuss realistic expectations for your situation.
Can I switch from Mounjaro to Wegovy or vice versa?
Switching between medications is possible but must be managed by your prescriber. There is no official conversion chart—your prescriber will assess the best approach. Never switch medications independently.
How do I know which one my GP will prescribe?
Your GP or prescriber will assess your medical history, other medications, BMI, comorbidities, and personal circumstances. Both require a clinical assessment. Ask your prescriber to discuss the rationale if either is recommended.
Are both available on the NHS?
Both Mounjaro and Wegovy are licensed in the UK. NHS access is through specialist tier 3 weight management services and varies significantly by region. Private prescription access is also available through GPhC-registered online pharmacies following clinical assessment. ```
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.