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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How Much Is 15mg Mounjaro Compared to Wegovy?
15mg is the maximum Mounjaro dose, and it's often compared to Wegovy 2.4mg (Wegovy's top dose) for weight management in the UK. However, they work differently — Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1 agonist only. Clinical trial data shows different average weight loss results at their respective maximum doses. Both are prescription-only medicines requiring clinical assessment. This guide explains the key differences to help you understand what these doses mean for weight management.
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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.
Mounjaro 15mg vs Wegovy 2.4mg — Mechanisms and Trial Data
Mounjaro (tirzepatide) 15mg is the maximum dose available. In the SURMOUNT-1 clinical trial, participants on 15mg lost an average of approximately 20.9% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) 2.4mg is the maximum maintenance dose. In the STEP-1 clinical trial, participants on 2.4mg achieved an average weight loss of approximately 14.9% of their body weight over 68 weeks, also with lifestyle changes.
The key difference: Mounjaro activates two hormone pathways (GIP and GLP-1), while Wegovy activates only the GLP-1 pathway. This dual mechanism may explain Mounjaro's slightly higher average weight loss in trials. However, individual results vary significantly — these are population averages, not assured outcomes.
Both require a tirzepatide or semaglutide prescription from a licensed prescriber following clinical assessment.
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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.
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Dose Equivalence and Individual Suitability
There is no official dose conversion chart between Mounjaro and Wegovy — they are different medications with different potencies. Clinically, 15mg Mounjaro is sometimes considered approximately equivalent to Wegovy 2.4mg in terms of effect, but this is not formal guidance.
Your prescriber will assess which medication suits you individually based on your health history, BMI, weight-related conditions, and any contraindications. Some patients may start Mounjaro, others Wegovy. Some may switch between them under medical supervision, which requires a prescriber's guidance on timing and transition.
Both are available through NHS specialist weight management services or private online prescribing with a UK-licensed prescriber. Try our GLP-1 weight loss calculator to see projected weight loss at different doses, and use our BMI calculator to assess your current health context.
- 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 15mg Mounjaro stronger than Wegovy 2.4mg?
Not necessarily "stronger" — they work via different mechanisms. Mounjaro is a dual GIP+GLP-1 agonist; Wegovy is GLP-1 only. Clinical trials showed Mounjaro 15mg had a higher average weight loss (20.9%) than Wegovy 2.4mg (14.9%), but individual results vary. Your prescriber will recommend the most suitable medication for you.
Can you switch from Wegovy to 15mg Mounjaro?
Yes, but only under prescriber guidance. Switching between medications requires proper medical assessment and timing. There is no standard conversion dose. Your prescriber will advise on whether a switch is appropriate and how to manage the transition safely.
How long does it take to reach 15mg Mounjaro?
Mounjaro is titrated gradually: starting at 2.5mg, then increasing by 2.5mg every 4 weeks up to 15mg. This usually takes around 20 weeks. Slower titration reduces nausea and allows your body to adjust. Your prescriber may adjust this timeline based on your tolerance.
What are the side effects of 15mg Mounjaro vs Wegovy?
Both commonly cause nausea, diarrhoea, vomiting, and stomach pain — especially during dose escalation. These typically improve over time. Side effect profiles are similar, though individual experiences vary. Report any concerning symptoms to your prescriber immediately.
Is Mounjaro 15mg available on the NHS in the UK?
Yes, NICE has approved tirzepatide (Mounjaro) for use in NHS specialist weight management services. However, NHS availability varies significantly by region and waiting lists can be lengthy. Private prescribing via UK-licensed online prescribers is also available.
Ready to take control of your weight loss journey?
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