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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Mounjaro 15mg Pen — UK NHS Prescription Guide
The Mounjaro 15mg pen is the highest dose of tirzepatide available in the UK for weight management. This is the maximum maintenance dose prescribed after a 20-week dose escalation process. Understanding NHS access routes, eligibility criteria, and what the 15mg dose can achieve is essential if you're considering this treatment. The journey to 15mg involves gradual dose increases, each held for at least four weeks. This page explains NHS access, private routes, and what clinical data shows about outcomes at this maximum dose in UK adults.
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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.
NHS Access and Eligibility for Mounjaro 15mg in the UK
NHS access to Mounjaro 15mg is available through tier 3 specialist weight management services, but availability varies significantly by region. Most NHS integrated care boards (ICBs) now include tirzepatide in their weight management pathways following NICE approval, though waiting lists can be substantial in many areas. To be eligible for NHS Mounjaro, you typically need a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, hypertension, or sleep apnoea. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower thresholds (BMI 27.5 and above) may apply due to higher cardiovascular risk at lower weights. Reaching the 15mg dose requires commitment: you start at 2.5mg, increase by 2.5mg every four weeks, and typically reach 15mg by week 20–21. Not all patients escalate to 15mg; some stabilise at lower doses. Your prescriber will assess whether escalation is appropriate based on your response and tolerance. NHS prescription access eliminates cost, but involves a referral from your GP to specialist services and potentially lengthy waiting times depending on your region.
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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.
Private Access and Mounjaro 15mg Cost in the UK
Private access to Mounjaro 15mg is available through GPhC-registered online pharmacies following a consultation with a UK-licensed prescriber. This route bypasses NHS waiting lists but involves out-of-pocket costs. At the maximum 15mg dose, monthly costs typically range from £280–£320, depending on the provider. Private prescribers assess the same eligibility criteria as NHS services—BMI, weight-related health conditions, and medical history. The advantage of private access is speed: if approved following your online consultation, you can begin treatment within days rather than waiting months for NHS tier 3 services. However, private prescribing still requires a legitimate clinical assessment; you cannot simply purchase Mounjaro without a prescription. Many UK adults use the private route to start treatment while on NHS waiting lists, or continue privately after NHS treatment. Your GP should be informed of any private treatment you're receiving, as medication interactions and monitoring remain important for your health and safety.
- 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.
How long does it take to reach the Mounjaro 15mg dose?
It takes approximately 20–21 weeks to reach the 15mg maintenance dose, starting from 2.5mg. Each dose is held for at least four weeks before increasing by 2.5mg increments. This gradual escalation allows your body to adjust and helps your prescriber monitor side effects and tolerance.
Is the 15mg Mounjaro dose more effective than lower doses?
Clinical data shows dose-dependent weight loss: 15mg achieved approximately 20.9% average body weight loss in trials, compared to around 15% at 5mg. However, individual results vary significantly. Some patients achieve their target weight loss at lower doses and may not escalate to 15mg.
Can I get Mounjaro 15mg on the NHS in my area?
Availability varies by region. NICE has approved tirzepatide for NHS use, but not all ICBs have implemented it yet, and waiting lists differ. Contact your GP to request a referral to your local tier 3 weight management service to check eligibility and availability.
What happens if I experience side effects at 15mg?
If you experience intolerable side effects at 15mg, discuss this with your prescriber immediately. You may reduce to a lower dose that you tolerate better. Weight management is a long-term process, and finding the right dose is more important than reaching the maximum.
Can I use our GLP-1 weight loss calculator to estimate results at 15mg?
Yes—our free GLP-1 weight loss calculator allows you to input the 15mg dose and estimate potential weight loss based on your starting weight. Remember that actual results vary by individual, and the calculator provides a projection based on clinical trial data, not a assures.
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.