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
How Many Ml in a Mounjaro Pen?
A Mounjaro KwikPen does not contain a fixed volume in millilitres — instead, each pre-filled pen delivers a specific dose in milligrams. The pen is designed to dispense 0.5 ml per injection, which varies in concentration depending on your dose strength. Each KwikPen contains four weeks' worth of doses (four injections), and the pens themselves are colour-coded by dose to help you identify your strength. Understanding how your Mounjaro pen works is essential for safe, effective use in your UK weight management journey.
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.
Mounjaro Pen Doses and What's Inside
Mounjaro comes in six colour-coded KwikPen strengths:
- 2.5 mg (light blue) — starting dose
- 5 mg (teal) — first maintenance dose
- 7.5 mg (navy) — escalation dose
- 10 mg (purple) — escalation dose
- 12.5 mg (pink) — escalation dose
- 15 mg (burgundy) — maximum dose
Each KwikPen contains a solution concentration of 2.5 mg/0.5 ml, meaning the 0.5 ml injection volume remains the same regardless of your dose — the medication strength changes, not the injection volume. Each pen holds four pre-filled doses (a four-week supply), and the needle is automatically covered after use for safety. The tirzepatide solution is a clear, colourless liquid designed for subcutaneous injection into the stomach, upper thigh, or upper arm. Always store your pens in the refrigerator at 2–8°C until first use.
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.
NHS Mounjaro Eligibility and UK Prescribing Context
In the UK, Mounjaro (tirzepatide) is prescribed through NHS tier 3 specialist weight management services following NICE approval. You'll need a BMI of 30 kg/m² or above, or 27–29.9 with weight-related health conditions like type 2 diabetes or cardiovascular disease, to be eligible. Access through the NHS involves referral from your GP and assessment by a specialist team — availability varies significantly by region. Private prescribing is also available through registered online prescribers following a clinical assessment. Whichever route you take, your healthcare provider will explain your dosing schedule and help you progress through the dose titration plan over 16–20 weeks to your optimal maintenance dose. Use our GLP-1 weight loss calculator to explore potential outcomes alongside your treatment plan.
- 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.
How much liquid is actually in a Mounjaro pen?
Each Mounjaro KwikPen delivers exactly 0.5 ml per injection. The pen contains four 0.5 ml doses (2 ml total) and is colour-coded by dose strength from 2.5 mg up to 15 mg. The volume stays the same — only the concentration changes.
Why do different Mounjaro doses have different coloured pens?
Colour coding helps you identify your dose strength quickly and reduces the risk of accidental dosing errors. Light blue is 2.5 mg, teal is 5 mg, through to burgundy for 15 mg. Always check the colour before injecting.
Can you refill a Mounjaro KwikPen?
No, Mounjaro KwikPens are single-use, pre-filled devices. Once you've used all four doses (four weeks), you dispose of the pen safely and use a new one. Never attempt to refill or reuse a pen.
What's the difference between Mounjaro and Wegovy injection volumes?
Both Mounjaro and Wegovy use once-weekly injections, but Wegovy pens deliver different volumes depending on dose strength, whereas Mounjaro pens always deliver 0.5 ml. Both are prescription-only and require clinical assessment before prescribing.
How should I store a Mounjaro pen before first use?
Store unopened Mounjaro pens in a refrigerator at 2–8°C in their original carton to protect from light. Do not freeze. Once you've used a pen for the first time, it can be kept at room temperature (below 30°C) for up to 30 days.
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.