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 — UK Prescribing and Availability Guide
Mounjaro 15mg is the maximum dose of tirzepatide available in the UK for weight management. It's a prescription-only medicine that requires clinical assessment before prescribing. Availability depends on whether you access treatment through the NHS or private online prescribing. Understanding your eligibility, the titration process to reach 15mg, and what this dose involves will help you navigate your weight management options in the UK healthcare system.
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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
Mounjaro on the NHS: NICE (National Institute for Health and Care Excellence) has approved tirzepatide (Mounjaro) for weight management within NHS specialist services. However, NHS access is primarily through tier 3 and tier 4 specialist weight management services, not routine GP prescription. You typically need referral from your GP to these services, and eligibility includes a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, hypertension, or obstructive sleep apnoea.
- South Asian, Chinese, Black African, and Black Caribbean adults may qualify at lower BMI thresholds (27.5 or above)
- Availability varies significantly by region and local integrated care board (ICB) decisions
- Waiting times for NHS specialist services can be several months in many areas
- The 15mg dose represents the maximum therapeutic dose after dose titration
Check with your local NHS weight management service about current availability and waiting times in your area.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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 Prescribing and the 15mg Dose Journey
Outside the NHS, Mounjaro is available through GPhC-registered online pharmacies following a clinical assessment by a UK-licensed prescriber. You don't need NHS referral for the private route. Reaching the 15mg dose takes time: you start at 2.5mg and increase by 2.5mg every 4 weeks, meaning it takes at least 20 weeks (approximately 5 months) to reach the maximum dose safely. Use our GLP-1 weight loss calculator to estimate potential outcomes at different doses, and our BMI calculator to understand your current health context. Private costs vary by dose and provider, typically ranging from £129–£320 monthly depending on your dose level.
- 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.
Can you jump straight to Mounjaro 15mg, or do you have to titrate from a lower dose?
No, you cannot start at 15mg. Dose titration is medically necessary — you begin at 2.5mg and increase by 2.5mg every 4 weeks. This minimises nausea and gastrointestinal side effects, and allows your body to adjust. Reaching 15mg safely takes approximately 20 weeks minimum. Any prescriber will follow this protocol.
Is Mounjaro 15mg available on the NHS right now?
Mounjaro (tirzepatide) is approved by NICE for NHS use, but availability depends on your local integrated care board (ICB) and whether you can access a tier 3 specialist weight management service. Many areas have long waiting lists. Private prescribing may offer faster access. Contact your GP or local weight management service for current availability in your area.
What's the difference between Mounjaro 15mg and Wegovy in terms of maximum dose?
Mounjaro's maximum dose is 15mg once weekly, whilst Wegovy's maximum is 2.4mg once weekly. Mounjaro uses a dual GIP and GLP-1 mechanism, whilst Wegovy is a GLP-1-only medication. Clinical trials showed Mounjaro may produce slightly higher average weight loss, but individual results vary significantly. Your prescriber will advise which is more suitable.
How long does it take to see weight loss results at the 15mg dose?
Weight loss results typically become more pronounced as you reach higher doses, but the timeline varies. Most people see noticeable changes between weeks 12–20 of treatment. The 15mg dose represents the maximum therapeutic effect, but reaching it takes approximately 5 months. Alongside reduced-calorie diet and increased physical activity, sustainable results develop over several months.
Are there any additional risks or side effects at the 15mg Mounjaro dose compared to lower doses?
The common side effects (nausea, diarrhoea, constipation) typically reduce as your body adjusts over time — paradoxically, many people experience fewer GI side effects at higher doses after weeks at the previous dose. However, serious side effects (severe stomach pain suggesting pancreatitis, gallbladder issues, allergic reactions) require immediate medical attention at any dose. Your GP or prescriber should monitor you throughout treatment.
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.