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
Free tracker included with every download this week
Mounjaro 15mg: UK's Maximum Dose Explained
Mounjaro 15mg is the highest dose available of this prescription weight management injection in the UK. Most people taking Mounjaro start at 2.5mg and gradually increase over several months to reach 15mg, with each dose held for a minimum of four weeks. The 15mg dose delivers the strongest effect of the dual GIP and GLP-1 receptor mechanism. Whether you need to reach 15mg depends on your individual response and what your prescriber assesses as right for you. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
How the Dose Titration to 15mg Works
Mounjaro follows a stepped dose titration schedule, meaning you don't start at 15mg — you build up gradually. Each KwikPen contains four weekly injections. Here's the typical pathway:
- Weeks 1–4: 2.5mg — starting dose for adjustment tolerance
- Weeks 5–8: 5mg — first maintenance increase
- Weeks 9–12: 7.5mg — further escalation
- Weeks 13–16: 10mg — mid-range dose
- Weeks 17–20: 12.5mg — near-maximum
- Week 21+: 15mg — maximum licensed dose
You must stay on each dose for at least four weeks before increasing, allowing your body to adjust and your prescriber to assess your response. Many people experience meaningful weight loss at lower doses (5–10mg) and may not need to progress to 15mg. Your prescriber will help determine the right dose for you.
Clinically BackedWeight Loss
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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.
Expected Weight Loss at 15mg and Side Effects
In the SURMOUNT-1 clinical trial, participants taking Mounjaro 15mg achieved an average weight loss of approximately 20.9% of their body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity. This represents significant results, though individual outcomes vary widely. Common side effects at any dose — including 15mg — include nausea, diarrhoea, vomiting, and constipation, typically most noticeable when first starting or increasing dose. These often improve within days or weeks. You can track your progress with our free progress tracker to monitor your results over time. Always report persistent or severe side effects to your prescriber immediately.
- 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.
Does everyone need to reach 15mg Mounjaro?
No. Many people achieve effective weight loss at lower doses like 5mg, 10mg, or 12.5mg. Your prescriber will assess your response at each dose and may keep you at a lower dose if it's working well for you. 15mg is the maximum available, not a target everyone must reach.
How long does it take to reach 15mg Mounjaro?
The standard titration schedule takes approximately 20–21 weeks (5 months) to progress from 2.5mg to 15mg, assuming you increase dose every 4 weeks. Some people may progress faster or slower depending on prescriber guidance and your response.
What's the difference between 15mg Mounjaro and other doses?
Clinical trials showed 15mg Mounjaro produced the greatest average weight loss (approximately 20.9% body weight), compared to about 15% at 5mg. However, the difference between 10mg and 15mg is smaller than between lower doses, and side effects may increase at higher doses.
Can I start Mounjaro at 15mg, or must I titrate up?
You must start at 2.5mg and titrate gradually. Starting at 15mg would carry significant risk of severe nausea, vomiting, and other side effects. The stepped approach allows your body to adapt and your prescriber to monitor your response safely.
Is Mounjaro 15mg available on the NHS in the UK?
Mounjaro is NICE-approved and available through NHS specialist tier 3 weight management services, but access varies significantly by region and NHS ICB. Waiting lists can be lengthy. Private online prescribing services can offer faster access to all doses, including 15mg, following a clinical assessment.
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.