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 MLs Are In Each Mounjaro Dose?
Each Mounjaro KwikPen dose delivers between 0.5ml and 1.5ml depending on your dose strength, though the exact volume varies slightly by individual dose. In the UK, Mounjaro is available as a once-weekly injection in doses ranging from 2.5mg to 15mg, delivered via a pre-filled KwikPen auto-injection device. This guide explains Mounjaro dosing in the UK context, how the KwikPen works, and what to expect when prescribed this tirzepatide injection for weight management through NHS or private prescribing routes.
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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 Dose Volumes and KwikPen Delivery
Mounjaro is administered as a once-weekly subcutaneous injection using the KwikPen device. Each dose delivers the following approximate volumes:
- 2.5mg dose: approximately 0.5ml
- 5mg dose: approximately 0.75ml
- 7.5mg dose: approximately 1ml
- 10mg dose: approximately 1.25ml
- 12.5mg dose: approximately 1.4ml
- 15mg dose: approximately 1.5ml
The KwikPen is pre-filled and single-use — you do not measure or draw the dose yourself. Simply press the injection button and the device automatically delivers the correct volume for your prescribed strength. Each KwikPen contains 4 weeks' worth of doses (4 individual injections), so you receive a new pen every month. The needle is very fine (29-gauge) and injection takes only a few seconds.
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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.
NHS Eligibility and Mounjaro Prescribing in the UK
In the UK, Mounjaro (tirzepatide) is available through NHS specialist weight management services (tier 3) following NICE approval. You must be referred by your GP to a specialist service — it is not routinely prescribed in general practice. Eligibility criteria include a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. For South Asian, Chinese, Black African, and Black Caribbean adults, lower BMI thresholds may apply. NHS waiting times vary significantly by region and can be lengthy in some areas. Private routes through GPhC-registered online prescribers offer faster access but require payment. Calculate your BMI using our free BMI calculator to check your eligibility threshold.
- 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.
Why does Mounjaro volume vary with dose strength?
Mounjaro is supplied as a concentrated liquid solution. Higher doses contain more of the active ingredient (tirzepatide) dissolved in slightly larger volumes of liquid. The KwikPen is calibrated so that pressing the injection button delivers exactly the right amount of solution for each dose strength — you do not need to worry about measuring it yourself.
Can I store a Mounjaro KwikPen after opening?
Yes. An unopened KwikPen must be refrigerated at 2–8°C. Once you inject your first dose, you can store the same pen at room temperature (below 30°C) for up to 30 days. After 30 days of room temperature storage, you must dispose of the pen even if doses remain. Always keep it away from direct heat and sunlight.
What if I accidentally inject more than my prescribed dose?
Each KwikPen is pre-filled with exactly one dose — you cannot accidentally inject more from a single pen. However, if you have concerns about injection volume or think something went wrong, contact your prescriber or NHS 111 for guidance. Never attempt to use the same KwikPen twice or "top up" a dose.
Is Mounjaro available on the NHS for everyone?
No. NHS access is through specialist tier 3 weight management services following referral from your GP and clinical assessment. Availability varies significantly by region and NHS ICB (Integrated Care Board). Many areas have long waiting lists. Your GP can explain local NHS options or discuss private prescribing alternatives if NHS access is delayed.
How does Mounjaro dosing compare to Wegovy?
Mounjaro (tirzepatide) is a dual GIP/GLP-1 agonist with doses up to 15mg weekly, while Wegovy (semaglutide) is a single GLP-1 agonist with doses up to 2.4mg weekly. Mounjaro volumes are larger (up to 1.5ml) because it contains a different formulation. Both use once-weekly KwikPen injections, but they are not interchangeable — your prescriber will assess which is suitable for you.
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.