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 licensed dose of Mounjaro (tirzepatide) available in the UK. This is the highest dose used in weight management treatment and is typically reached after gradual dose escalation over several months. At this dose, clinical trials showed participants achieved an average weight loss of around 20.9% of their body weight. However, individual results vary significantly, and not everyone needs or reaches this dose. Your GP or prescriber will assess the appropriate dose for you based on your response to treatment and tolerability.
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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/mΒ²).
While BMI isn't a perfect measure β it doesn't account for muscle mass, bone density, or fat distribution β 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 β 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 Escalation and the 15mg Maximum
Mounjaro is prescribed using a dose titration schedule, meaning you start at a low dose and gradually increase every 4 weeks if tolerated:
- Weeks 1β4: 2.5mg (starting dose)
- Weeks 5β8: 5mg
- Weeks 9β12: 7.5mg
- Weeks 13β16: 10mg
- Weeks 17β20: 12.5mg
- Week 21+: 15mg (maximum dose)
Most people do not reach 15mg immediately. Your prescriber may keep you on a lower maintenance dose if you achieve good results or experience side effects. The 15mg dose from a Mounjaro KwikPen is injected once weekly. Reaching 15mg typically takes 5β6 months of treatment, and some patients find lower doses equally effective for their goals.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care β 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 β 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 β completely free.
Weight Loss Results at 15mg Dose
In the SURMOUNT-1 clinical trial, participants on 15mg Mounjaro achieved an average weight loss of 20.9% of their body weight over 72 weeks. This was accompanied by a reduced-calorie diet and increased physical activity. For example, someone weighing 100kg might lose approximately 21kg on average β though results vary considerably between individuals. Some people lose more, some less. Weight loss tends to continue gradually throughout treatment, and the 15mg dose is used for long-term weight management, not just rapid initial loss. Our GLP-1 weight loss calculator can help you estimate potential results at different doses based on your starting weight.
- 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 β 5mg β 7.5mg β 10mg β 12.5mg β 15mg
- GLP-1 receptor agonist
- Up to 15β17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg β 0.5mg β 1mg β 1.7mg β 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 | 15β22.5% | 12β17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20β32 weeks | 16β20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | Β£150βΒ£250/month | Β£150βΒ£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 β 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 I start Mounjaro at 15mg?
No. Mounjaro always starts at 2.5mg and increases gradually over weeks to reach 15mg. Starting at the maximum dose would cause severe side effects like nausea and vomiting. The gradual approach allows your body to adapt. Your prescriber will manage the escalation schedule based on your tolerance and response.
Is 15mg Mounjaro available on the NHS in the UK?
Mounjaro is available through NHS specialist weight management services (tier 3/4), but access varies significantly by region and is subject to local commissioning decisions. Waiting lists can be long. Privately, 15mg Mounjaro is available through UK-licensed online prescribers following a clinical assessment. Discuss NHS options with your GP first.
What are the side effects at 15mg Mounjaro?
Side effects at 15mg may include nausea, diarrhoea, vomiting, and constipation β similar to lower doses but potentially more pronounced. Most people experience fewer side effects over time as their body adapts. Serious side effects like severe stomach pain or allergic reactions are rare but require immediate medical attention.
How does 15mg Mounjaro compare to Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. The maximum Mounjaro dose of 15mg and maximum Wegovy dose of 2.4mg are not directly comparable. Mounjaro generally showed slightly higher average weight loss in trials, but individual results vary. Your prescriber will choose based on your health profile.
What happens if 15mg Mounjaro doesn't work for me?
If you're not losing weight or hitting a plateau on 15mg, your prescriber may recommend continuing β weight loss often resumes after plateaus. Alternatively, they may suggest lifestyle adjustments (diet/exercise changes) or consider switching medication. Discuss concerns with your prescriber; dosage changes are not recommended beyond 15mg.
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.