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 In A Mounjaro Dose?
Each Mounjaro KwikPen is a pre-filled injection device containing multiple doses. The volume of each dose depends on the strength: doses range from 2.5 mg to 15 mg, with each pen containing 4 weeks' worth of weekly injections. The exact ml volume varies slightly by dose strength, but each individual injection delivers approximately 0.5 ml of solution. Mounjaro is a prescription-only medicine available in the UK through NHS specialist services or private prescribing following a clinical assessment.
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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.
Understanding Mounjaro KwikPen Dose Volumes
Mounjaro comes as a pre-filled KwikPen injection device, and each pen contains four weekly doses. The ml volume delivered in each individual injection is consistent across all dose strengths — approximately 0.5 ml per weekly dose. However, the concentration of tirzepatide varies: a 2.5 mg dose, 5 mg dose, 7.5 mg dose, 10 mg dose, 12.5 mg dose, and 15 mg dose all contain different amounts of the active ingredient dissolved in that 0.5 ml volume.
Each KwikPen is colour-coded by dose strength to help prevent dosing errors. The pen displays a dose selector dial so you can confirm your prescribed dose before injecting. Once you've used all four doses from one pen (four weeks), you'll need a new prescription to obtain the next month's supply.
- Each KwikPen contains 4 weekly injections (one month supply)
- Each individual injection is approximately 0.5 ml
- The dose concentration (2.5 mg to 15 mg) determines the strength, not the volume
- Pens are colour-coded by dose strength for safety
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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 Dose Titration and Prescription Information
Treatment with Mounjaro begins with a 2.5 mg starting dose for the first four weeks, then typically escalates every four weeks if tolerated. Most people progress through 5 mg, 7.5 mg, 10 mg, 12.5 mg, and ultimately 15 mg (the maximum dose). Each dose increase requires a new KwikPen prescription. In the UK, Mounjaro is available through NHS tier 3 specialist weight management services or private online prescribing from a GPhC-registered pharmacy following a clinical assessment. Your prescriber will determine your starting dose and escalation schedule based on your individual health, BMI, and any weight-related health conditions. Use our free GLP-1 weight loss calculator to explore potential weight loss outcomes at different doses.
- 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 ml volume the same for all Mounjaro doses?
Yes, each Mounjaro injection is approximately 0.5 ml regardless of dose strength. The difference between doses (2.5 mg to 15 mg) is the concentration of tirzepatide dissolved in that volume, not the volume itself. Each pen is colour-coded to match the dose strength.
How long does one Mounjaro KwikPen last?
One KwikPen contains four weekly injections, so it lasts for four weeks (one month). After four weeks, you'll need a new prescription and pen for the next month's supply. Store unopened pens in the fridge at 2–8°C.
Do I need a prescription to get Mounjaro in the UK?
Yes, Mounjaro is prescription-only in the UK. You can access it through NHS specialist tier 3 weight management services (usually via GP referral) or through private prescribing from a UK-licensed prescriber. A clinical assessment is required to confirm eligibility.
What's the difference between Mounjaro (tirzepatide) and Wegovy (semaglutide)?
Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1 agonist only. Mounjaro doses range from 2.5–15 mg weekly, Wegovy from 0.25–2.4 mg weekly. Both are once-weekly injections. Clinical trials showed Mounjaro users lost approximately 15–21% body weight on average.
Can I store a Mounjaro KwikPen outside the fridge after I start using it?
Yes, after the first injection, you can store the pen at room temperature (below 30°C) for up to 30 days. Always keep it away from heat and direct sunlight. Discard the pen after 30 days from first use, even if insulin remains.
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