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 15 mg Mounjaro vs Wegovy?
15 mg is the maximum dose of Mounjaro (tirzepatide) available in the UK. If you're comparing it to Wegovy, understanding the differences matters for your GP or prescriber's assessment. Both are prescription-only GLP-1 medications licensed for weight management, but they work slightly differently and have different dose ranges. This guide explains what 15 mg Mounjaro represents, how it compares to Wegovy's maximum dose, and what clinical evidence shows about weight loss at these doses.
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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 15 mg vs Wegovy 2.4 mg — Clinical Trial Data
15 mg Mounjaro is the maximum dose available in the UK, taken once weekly via KwikPen injection. In the SURMOUNT-1 clinical trial, participants on 15 mg Mounjaro achieved an average weight loss of approximately 20.9% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity.
Wegovy's maximum dose is 2.4 mg weekly, and STEP-1 trial data showed average weight loss of around 14.9% body weight at this dose over 68 weeks under similar lifestyle conditions.
- Mounjaro mechanism: Dual GIP + GLP-1 receptor agonist (activates two hormone pathways)
- Wegovy mechanism: GLP-1 receptor agonist only (single pathway)
- Important: Clinical trial averages vary significantly between individuals — results are not assured
Your GP or licensed prescriber will assess which medication, if any, suits your individual health profile and eligibility.
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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 Titration and Suitability — Individual Assessment Required
15 mg Mounjaro is reached gradually through a dose titration schedule (starting at 2.5 mg and increasing every 4 weeks). Not everyone reaches the maximum dose — many people stabilise at lower doses like 10 mg or 12.5 mg. Wegovy similarly escalates from 0.25 mg to 2.4 mg over approximately 16–20 weeks.
Whether 15 mg Mounjaro or 2.4 mg Wegovy is prescribed depends on your individual response, tolerability, and clinical suitability. Both require an NHS specialist referral or private clinical assessment. Our free GLP-1 weight loss calculator can help you understand potential weight loss outcomes at different doses, but a prescriber's assessment is essential before any prescription. Weight management injections are prescribed alongside lifestyle changes, never as a substitute for them.
- 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 15 mg Mounjaro better than Wegovy 2.4 mg?
Clinical trials show Mounjaro 15 mg achieved slightly higher average weight loss (20.9%) compared to Wegovy 2.4 mg (14.9%), but individual results vary significantly. "Better" depends on your personal health profile, eligibility, tolerability, and prescriber assessment. Both are effective prescription medications requiring clinical evaluation.
How do you get to 15 mg Mounjaro?
Mounjaro starts at 2.5 mg and increases by 2.5 mg every 4 weeks if tolerated: 2.5 mg → 5 mg → 7.5 mg → 10 mg → 12.5 mg → 15 mg. Each dose is a weekly injection via KwikPen. Not everyone needs or reaches 15 mg — your prescriber will determine the right dose for you.
What's the difference between Mounjaro and Wegovy mechanisms?
Mounjaro (tirzepatide) activates two hormone pathways: GIP and GLP-1. Wegovy (semaglutide) activates GLP-1 only. This dual action in Mounjaro may contribute to its higher average weight loss in trials, though both work by reducing appetite and supporting feeling fuller after meals.
Can you get Mounjaro 15 mg on the NHS in the UK?
Mounjaro is available through NHS tier 3 specialist weight management services following assessment and referral from your GP. Availability and wait times vary significantly by region. Private prescribing through licensed online providers is also an option without NHS referral.
What side effects occur at 15 mg Mounjaro?
Common side effects include nausea, diarrhoea, constipation, and stomach pain—similar at all doses but potentially more frequent at higher doses. Serious side effects are rare but can include severe stomach pain (pancreatitis risk) or gallbladder problems. Always discuss side effect concerns with your GP. ```
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