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?
15mg is the maximum dose of Mounjaro (tirzepatide) available in the UK. This is the highest strength that can be prescribed once weekly following a full dose titration schedule. Most patients reach 15mg after gradually increasing from the starting dose of 2.5mg over approximately 4–5 months. The 15mg dose is prescribed as a single injection using the Mounjaro KwikPen device. Whether you reach this dose depends on your individual response, tolerance, and clinical assessment by your prescriber. Use our free GLP-1 weight loss calculator to explore how different doses may affect potential outcomes.
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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.
Mounjaro Dose Titration and 15mg in Context
Mounjaro dosing follows a structured dose titration schedule, starting at 2.5mg and increasing every 4 weeks if tolerated. The progression is: 2.5mg (weeks 1–4) → 5mg (weeks 5–8) → 7.5mg (weeks 9–12) → 10mg (weeks 13–16) → 12.5mg (weeks 17–20) → 15mg (week 21 onwards). Not all patients reach 15mg; many achieve good results at 5mg, 10mg, or 12.5mg. Clinical trials show that average weight loss increases with higher doses, but individual responses vary significantly. In the SURMOUNT-1 trial, participants on 15mg lost approximately 20.9% of body weight on average over 72 weeks, compared to 15% on 5mg — though this was alongside a reduced-calorie diet and increased physical activity. Your prescriber will assess whether escalation to 15mg is appropriate based on your tolerance, side effects, and clinical response. Access to Mounjaro through NHS specialist weight management services may differ from private prescribing routes in terms of dose progression protocols.
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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.
NHS Access and 15mg Mounjaro in the UK
NHS eligibility for Mounjaro (tirzepatide) has been approved by NICE for use within specialist weight management services in England. However, access varies significantly by region and ICB (Integrated Care Board). Waiting times for NHS specialist tier 3 services can be lengthy, sometimes several months to years depending on your area. Private prescribing offers faster access to Mounjaro through UK-licensed prescribers via GPhC-registered pharmacies, without requiring an NHS referral. Regardless of route, 15mg is only prescribed after clinical assessment confirms it is safe and appropriate for you. Your GP or private prescriber will consider your BMI, weight-related health conditions, previous dose tolerance, and any contraindications. Calculate your personal BMI using our free BMI calculator to understand your starting point for any weight management discussion.
- 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 available on the NHS in the UK?
Mounjaro has been approved by NICE for NHS use within specialist weight management services. However, availability, waiting times, and dose progression vary significantly by region and ICB. Your GP can refer you to a tier 3 weight management service, but NHS access to 15mg is not assured — it depends on clinical assessment and local provision.
What is the difference between 15mg Mounjaro and lower doses?
Clinical trials showed higher average weight loss at 15mg (~20.9%) compared to 5mg (~15%) over 72 weeks. However, many people achieve excellent results at lower doses with fewer side effects. The right dose for you is determined by your individual tolerance, response, and prescriber assessment — not everyone needs 15mg.
How long does it take to reach 15mg Mounjaro?
The standard titration schedule takes approximately 4–5 months to reach 15mg, starting from 2.5mg and increasing every 4 weeks. Each increase allows your body to adjust and helps your prescriber monitor for side effects. Your specific timeline may differ based on tolerance and clinical response.
Can I stop at a lower dose than 15mg Mounjaro?
Yes, absolutely. Many patients find that 5mg, 10mg, or 12.5mg gives them the results they want with side effects they can manage. Your prescriber can adjust or maintain your dose based on your individual needs — 15mg is the maximum available, not a requirement.
What are the side effects of 15mg Mounjaro?
Common side effects include nausea, diarrhoea, vomiting, and constipation — these may be more frequent at higher doses but often reduce over time. Serious side effects are rare and may include pancreatitis (severe stomach pain) or gallbladder problems. Always discuss side effect concerns with your prescriber.
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.