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 Can Mounjaro Stay in the Fridge?
Proper storage of your Mounjaro KwikPen is essential to keep it safe and effective. Unopened pens must be stored in a refrigerator at 2°C to 8°C and should never be frozen. Once you've started using a pen, you can keep it at room temperature below 30°C for up to 30 days before it needs to be disposed of. Understanding these storage requirements helps you manage your tirzepatide prescription safely and avoid waste. Let's walk through the complete storage guidance for Mounjaro in the UK, including what happens if your pen gets too warm or too cold, and how to recognise when it's no longer safe to use.
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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 Refrigerator Storage — Unopened Pens
Unopened Mounjaro pens must be stored in a refrigerator at 2°C to 8°C. Keep them in the original carton to protect from light exposure. At this temperature, unopened pens remain safe to use until the expiry date printed on the box — typically around 36 months from manufacture. Never freeze your Mounjaro KwikPen; if it freezes, the medication is damaged and you must not use it. Check the temperature of your fridge regularly to ensure it stays within the safe range. If you're travelling or moving house, use a cool bag or insulated travel case to maintain the correct temperature during transit. Keep pens away from direct sunlight and heat sources like radiators or cookers. If you're unsure whether a pen has been frozen, contact your pharmacy for guidance rather than risking using damaged medication.
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.
Room Temperature Storage and Disposal After First Use
Once you've opened and used a Mounjaro pen for the first time, you can store it at room temperature below 30°C for up to 30 days. After 30 days, you must dispose of the pen safely, even if it still contains medication — the formulation becomes less stable once opened. During this 30-day window, keep your pen away from heat and direct sunlight. At the end of the 30 days, place the used pen in a sharps bin or return it to your pharmacy for safe disposal. Never throw used pens in household waste or flush them down the toilet. If you miss a dose and remember more than 4 days later, skip that dose and continue your normal weekly schedule — do not use an old pen. Track your injection dates using our free progress tracker to help manage your Mounjaro schedule and storage rotation effectively.
- 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.
What temperature should I store unopened Mounjaro at?
Store unopened Mounjaro KwikPens in a refrigerator at 2°C to 8°C. Keep them in the original carton to protect from light. Check your fridge temperature regularly to ensure it stays within this safe range. Never freeze Mounjaro — if frozen, the medication is damaged and cannot be used.
Can I use Mounjaro if it's been frozen?
No. If your Mounjaro pen has been frozen, do not use it. The medication becomes unstable when frozen and will not work effectively. Contact your pharmacy for advice on what to do. They may help you obtain a replacement pen if needed.
How long can I keep Mounjaro at room temperature?
Once opened, Mounjaro can be stored at room temperature (below 30°C) for up to 30 days. After 30 days, you must dispose of the pen safely, even if it contains unused medication. Keep used pens away from heat and direct sunlight during this period.
What should I do with my used Mounjaro pen after 30 days?
Place your used pen in a sharps bin for safe disposal. Alternatively, return it to your pharmacy — most UK pharmacies have disposal bins for used injection devices. Never throw pens in household waste or flush them down the toilet.
How do I know if my Mounjaro has been damaged by heat or cold?
Visual signs include cloudiness in the liquid, particles, or discolouration. If you're unsure, contact your pharmacy before using the pen. Never use medication that looks abnormal. When in doubt, it's safer to get a replacement from your prescriber.
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.