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 Long Does Unopened Mounjaro Last?
Unopened Mounjaro KwikPen devices last for up to 3 years from the manufacture date if stored correctly in a refrigerator. The exact expiry date is printed on each pen's carton and label. Proper storage is essential to maintain the medicine's effectiveness — once you open a pen, it can only be kept for 30 days at room temperature. Understanding storage and shelf life is important if you're considering Mounjaro treatment through an NHS specialist service or private UK prescription route.
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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.
Unopened Mounjaro Storage Requirements
Unopened Mounjaro pens must be stored in a refrigerator at 2°C to 8°C to maintain their 3-year shelf life. Keep the KwikPen in its original carton to protect it from light exposure. Never freeze unopened pens — if a pen freezes, it becomes unusable and must be discarded.
The expiry date is printed clearly on the carton and the pen itself. Always check this date before use. Storage at room temperature above 8°C will significantly reduce the shelf life and may damage the medicine. If you're planning to order tirzepatide through a private UK prescription service, ensure your pharmacy stores stock properly and that your delivery arrives in good condition.
- Store unopened: refrigerator (2–8°C)
- Keep in original carton
- Shelf life: up to 3 years
- Never freeze
- Check expiry date before use
Clinically BackedWeight Loss
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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.
After Opening — What You Need to Know
Once you remove a Mounjaro KwikPen from the refrigerator for first use, it can be stored at room temperature (below 30°C) for up to 30 days. This 30-day window applies whether you use the pen once or store it without using it. After 30 days, the pen must be disposed of, even if it still contains medicine.
Each KwikPen contains 4 doses (4 weeks of injections). Plan your treatment schedule carefully — if you miss doses, you may not use all four injections within the 30-day window. Keep opened pens away from direct sunlight and heat. If an opened pen is accidentally refrigerated, you can return it to room temperature storage and continue using it within the remaining 30-day period.
- 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.
Can I reuse an unopened Mounjaro pen?
No. Each KwikPen is designed for single-patient use only and cannot be reused. Once the needle cover is removed and a dose is administered, that pen is considered opened. Unopened pens can only be used by the person they were prescribed to, and must be stored correctly to maintain effectiveness.
What happens if my unopened Mounjaro freezes?
If an unopened Mounjaro KwikPen is accidentally frozen, it must be discarded and not used. Freezing damages the medicine and makes it unsafe. Contact your prescriber or pharmacy immediately if this occurs — they can issue a replacement or advise on next steps for your treatment plan.
How do I know when my Mounjaro expires?
The expiry date is printed on the carton and directly on the KwikPen label. Always check this date before starting treatment. Your pharmacy will also inform you of expiry dates when dispensing. If you're unsure, ask your pharmacist — never use a pen past its expiry date.
Can I travel with unopened Mounjaro on an aeroplane?
Yes, unopened Mounjaro can be transported in a cool bag with ice packs in your hand luggage. You'll need a copy of your prescription or a letter from your prescriber. Check airline policies before travelling — rules vary. Some airlines require notification. Keep the pen in its original packaging and ensure it stays between 2–8°C during travel.
What's the difference between unopened Mounjaro shelf life and opened shelf life?
Unopened Mounjaro lasts up to 3 years if refrigerated properly. Once opened and used for the first injection, it can only be stored at room temperature for 30 days maximum. This shorter window applies regardless of how many injections you've taken from that particular KwikPen. ```
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.