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 Doses Are in a Mounjaro Pen?
Each Mounjaro KwikPen contains exactly 4 doses — enough for 4 weeks of once-weekly injections. This is the standard supply format for Mounjaro (tirzepatide), the prescription-only weight management injection licensed in the UK. Understanding your pen supply, storage requirements, and dose schedule is important for managing your treatment effectively.
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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 KwikPen Supply and Doses
Each Mounjaro KwikPen contains 4 pre-filled doses, with each dose delivered as a once-weekly injection. The pen is colour-coded to match your current dose strength, making it easy to identify which pen you're using during your titration schedule.
- 4 doses per pen = 4 weeks of treatment
- Once-weekly injection schedule
- Each dose between 2.5 mg and 15 mg (depending on your stage)
- Pre-filled, ready-to-use injector pen
- Colour-coded for easy identification
During your dose titration, you'll typically progress through different coloured pens as your dose increases every 4 weeks. Your prescriber will advise which pen strength you need each month, and you'll need to order or collect a new 4-dose pen each time you step up to the next dose level.
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.
Storing Your Mounjaro Pens Correctly
Proper storage is essential for Mounjaro safety and effectiveness. Unopened pens must be kept in the refrigerator at 2°C to 8°C in their original carton, protected from light. Never freeze a Mounjaro pen — if frozen accidentally, do not use it.
Once you've opened a pen and taken your first dose, you can store it at room temperature (below 30°C) for up to 30 days. After 30 days from first use, discard the pen safely even if doses remain. Keep pens away from direct heat and sunlight. Always check the expiry date before using any pen, and dispose of used pens according to your local clinical waste guidelines — ask your pharmacist for advice.
- 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 often do I use a Mounjaro pen?
Mounjaro is a once-weekly injection. You use one dose from your pen every 7 days. Since each pen contains 4 doses, a single pen lasts exactly 4 weeks. You'll need to order a new pen when your current one is empty.
Can I use my Mounjaro pen if it's been frozen?
No. Mounjaro must never be frozen. If your pen has been accidentally frozen, do not use it — discard it safely and contact your prescriber or pharmacy for a replacement. Always store unopened pens in the refrigerator between 2°C and 8°C.
What happens when I step up to a higher Mounjaro dose?
Each dose level has its own colour-coded pen. After 4 weeks on your current dose, you'll step up to the next level (unless you're already on the maximum 15 mg dose). Your prescriber will confirm when to order your next pen. You cannot split doses or adjust the pen yourself — each injection delivers a fixed, pre-measured amount.
How long can I keep my Mounjaro pen at room temperature?
Once you've opened a pen and taken your first injection, you can keep it at room temperature (below 30°C) for up to 30 days. After 30 days, discard the pen even if it contains unused doses. Unopened pens must stay refrigerated at 2°C to 8°C until first use.
Where can I get Mounjaro in the UK?
Mounjaro is prescription-only. In the UK, access is through NHS specialist weight management services (tier 3) or private online prescribing following a clinical assessment. Your GP can refer you to an NHS service, or you can consult a UK-licensed prescriber online. A healthcare professional must assess your eligibility based on your BMI and health history.
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.