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?
15 mg is the maximum dose of Mounjaro (tirzepatide) available in the UK. This prescription-only weight management injection reaches its highest dose after a gradual 20-week escalation process, starting from 2.5 mg. The 15 mg dose is delivered once weekly via a pre-filled KwikPen device. Not all patients require the maximum dose — your prescriber will assess whether stepping up to 15 mg is appropriate based on your individual response and tolerance. Understanding Mounjaro's dose progression and what 15 mg actually means will help you make informed decisions about this UK-licensed treatment option.
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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.
Mounjaro 15 Mg Dose — Escalation and UK Context
15 mg is the highest available dose of Mounjaro (tirzepatide) in the UK. Each dose is administered once weekly via a pre-filled KwikPen injection device. Reaching 15 mg takes approximately 20 weeks of gradual escalation from the starting dose of 2.5 mg. The dose progression follows a structured timetable: you remain on each dose level for a minimum of 4 weeks before your prescriber increases it. This staged approach allows your body to adapt and helps your prescriber monitor tolerability and effectiveness at each level.
- Week 1–4: 2.5 mg weekly
- Week 5–8: 5 mg weekly
- Week 9–12: 7.5 mg weekly
- Week 13–16: 10 mg weekly
- Week 17–20: 12.5 mg weekly
- Week 21+: 15 mg weekly (maximum dose)
Many patients achieve their target weight loss results at lower doses (such as 10 mg or 12.5 mg) and do not require escalation to the full 15 mg. Your prescriber will discuss whether continuing escalation is appropriate for you. The 15 mg dose is also equivalent to the higher end of semaglutide (Wegovy), though tirzepatide uses a dual GIP and GLP-1 mechanism rather than GLP-1 alone.
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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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15 Mg Mounjaro — NHS Eligibility and What to Expect
Accessing Mounjaro 15 mg in the UK depends on your route: NHS specialist tier 3 weight management services can prescribe Mounjaro following assessment, though availability and waiting times vary significantly by region. Private prescribing through a UK-licensed online provider is also available, where you'll be assessed and prescribed at the appropriate starting dose. Clinical trial data (SURMOUNT-1) showed that participants on the full 15 mg dose lost approximately 21% of their body weight on average — though individual results vary considerably. To check whether Mounjaro might be suitable for you, use our free GLP-1 weight loss calculator to estimate potential outcomes, and calculate your current BMI using our free BMI calculator to confirm eligibility criteria.
- 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 does 15 mg of Mounjaro actually do?
At 15 mg, Mounjaro (tirzepatide) works at its maximum strength as a dual GIP and GLP-1 receptor agonist. This activates two hormone pathways that may help reduce appetite, increase feelings of fullness, and support weight management alongside diet and exercise. Clinical trials showed approximately 21% average body weight loss at this dose, though results vary between individuals.
How long does it take to reach 15 mg Mounjaro?
It takes approximately 20 weeks (5 months) of gradual escalation to reach the 15 mg dose, starting from 2.5 mg. You spend a minimum of 4 weeks at each dose level, allowing your body to adjust before stepping up. Your prescriber may pause or extend any step if needed for tolerability.
Can I get 15 mg Mounjaro through the NHS?
Yes, Mounjaro is available through NHS specialist tier 3 weight management services following clinical assessment and referral. However, NHS availability and waiting times vary considerably by region (ICB). Private prescribing is also available through UK-licensed online providers without NHS referral.
Do I need to reach 15 mg, or can I stay on a lower dose?
You do not need to reach 15 mg. Many patients achieve good results at 10 mg, 12.5 mg, or lower doses. Your prescriber will assess your progress and tolerance at each step and discuss whether further escalation is appropriate for your individual needs and goals.
How does 15 mg Mounjaro compare to Wegovy?
15 mg Mounjaro is roughly equivalent to 2.4 mg Wegovy (semaglutide) in terms of weight loss outcomes, but they work differently. Mounjaro uses dual GIP and GLP-1 activation, while Wegovy uses GLP-1 alone. Both are prescription-only and require clinical assessment. Individual response varies, and your prescriber will recommend the best option for you.
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.