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 Many Ml In One Dose Of Mounjaro?
Mounjaro comes in a pre-filled KwikPen device, and each injection delivers a precise dose of tirzepatide. The volume injected remains the same across all dose strengths — what changes is the concentration of the active ingredient. Each KwikPen contains 1.5 ml of solution, delivering four weekly doses. Understanding how Mounjaro doses work, and how they compare to alternatives like Wegovy, helps you know what to expect if you're considering this prescription-only weight management injection in the UK.
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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 KwikPen Dose Volumes and Strength
Each Mounjaro KwikPen contains 1.5 ml of solution total, which is divided into four weekly injections of approximately 0.375 ml per dose. However, what matters clinically is not the volume injected but the milligrams (mg) of tirzepatide delivered. Doses range from 2.5 mg (starting dose) up to 15 mg (maximum). The pen is pre-filled and colour-coded by strength:
- 2.5 mg dose: light blue
- 5 mg dose: green
- 7.5 mg dose: red
- 10 mg dose: grey
- 12.5 mg dose: orange
- 15 mg dose: teal
Each pen lasts four weeks (one injection per week). You don't need to measure or adjust the volume — the KwikPen automatically delivers the correct amount. UK prescriptions specify the mg dose; the pharmacy dispenses the appropriately formulated pen.
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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.
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Mounjaro vs Wegovy: Dose Comparison
Wegovy (semaglutide) also uses pre-filled injection pens, but with different dose strengths. Wegovy starts at 0.25 mg and escalates to a maximum of 2.4 mg over approximately 16 weeks. In terms of mechanism, Mounjaro is a dual GIP and GLP-1 receptor agonist, whereas Wegovy is a GLP-1 agonist only — this difference in how they work, rather than injection volume, is what distinguishes them clinically. Clinical trial data (SURMOUNT for Mounjaro, STEP for Wegovy) showed average weight loss of approximately 15–21% for Mounjaro and approximately 15% for Wegovy at maximum doses. Both are prescription-only and require a clinical assessment before being prescribed. Your GP or prescriber will assess which is more suitable for your individual health profile.
- 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 the volume of a Mounjaro injection the same at every dose strength?
Yes. Each Mounjaro KwikPen delivers approximately 0.375 ml per injection, regardless of dose strength (2.5 mg to 15 mg). The volume stays constant; the concentration of active ingredient (tirzepatide) changes. The pen is pre-filled, so you don't need to measure or calculate — it automatically delivers the correct dose.
How long does one Mounjaro KwikPen last?
One KwikPen contains four weekly doses and lasts four weeks. After four injections, you dispose of the used pen and begin a new one if continuing treatment. Each pen is single-use only and cannot be refilled.
Can I switch between Mounjaro and Wegovy?
Switching between medications must always be managed by your prescriber. While approximate dose equivalences exist (e.g., Mounjaro 10 mg is roughly equivalent to Wegovy 1.7 mg), there is no official conversion chart. Any switch requires clinical guidance, and your prescriber will assess whether a transition is appropriate for your health.
What should I do if I miss a Mounjaro injection?
If you remember within 4 days of your missed dose, inject as soon as you remember, then continue your normal weekly schedule. If more than 4 days have passed, skip that dose and take your next injection on the normal scheduled day. Never take a double dose.
Is Mounjaro available on the NHS in the UK?
Yes, Mounjaro (tirzepatide) has been approved by NICE and is available through NHS specialist tier 3 weight management services. However, access varies significantly by region and waiting lists can be lengthy. You can also access Mounjaro privately through a UK-licensed prescriber following an online 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.