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 A Mounjaro Pen Last In The Fridge?
If you've been prescribed Mounjaro (tirzepatide) through the NHS or privately, proper storage is essential to keep your medication safe and effective. An unopened Mounjaro KwikPen can be stored in the fridge for its full shelf life — typically until the expiry date printed on the carton — as long as it's kept at the correct temperature. Once you start using a pen, the rules change. Understanding UK storage guidance helps you get the most from your prescription and avoid wasting medication.
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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 Storage Requirements — Temperature And Conditions
Unopened Mounjaro pens: Store in a refrigerator between 2°C and 8°C. Keep the pen in its original carton to protect it from light. Under these conditions, unopened pens remain safe to use until the expiry date on the packaging — typically three years from manufacture. Never freeze Mounjaro; if a pen has been frozen, it must be discarded and not used.
After first use: Once you've taken your first injection from a KwikPen, you can store it at room temperature — below 30°C — for up to 30 days. This makes it convenient to carry with you or keep at home without needing constant refrigeration during your treatment weeks. After 30 days from first use, dispose of the pen safely in a sharps bin, even if it contains remaining doses.
- Keep away from direct sunlight and heat sources
- Do not leave in a car or warm environment
- Ensure the pen cap is on when storing
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 Prescriptions And Private Mounjaro — Storage Still Applies
Whether you receive Mounjaro through an NHS tier 3 specialist weight management service or via private prescription following an online clinical assessment, the storage requirements are identical. Each KwikPen contains four weekly doses, so proper storage directly affects your treatment continuity. If you're receiving Mounjaro on the NHS, your specialist service should provide clear storage instructions; if prescribed privately, your pharmacy will include storage guidance with your delivery. Always check the patient information leaflet (PIL) included with your medication for any updates.
Use our GLP-1 weight loss calculator to track your projected weight loss alongside your treatment, and our progress tracker to log your actual results week by week.
- 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 Mounjaro be stored at in the fridge?
Unopened Mounjaro pens must be stored between 2°C and 8°C in a refrigerator. Keep them in the original carton to protect from light. Never freeze — frozen pens must be discarded. Once you start using a pen, it can be kept at room temperature (below 30°C) for up to 30 days.
How long can you keep an opened Mounjaro pen at room temperature?
After your first injection from a KwikPen, you can store it at room temperature (below 30°C) for up to 30 days maximum. After 30 days, the pen must be disposed of safely in a sharps bin, even if doses remain inside it.
Can you travel with Mounjaro and keep it cool?
Yes. Once opened, your Mounjaro pen can be kept at room temperature for up to 30 days, making it travel-friendly. Use a cool bag with ice packs if you prefer extra protection, but refrigeration is not required during this 30-day window. Do not freeze it during travel.
What should I do if my Mounjaro pen has been left out of the fridge?
If an unopened pen was accidentally left at room temperature for a short time, it's usually still safe if refrigerated promptly. However, if it's been above 30°C for extended periods or exposed to heat, contact your pharmacy or GP for advice. Never use a pen that has been frozen or exposed to extreme heat.
Do I need to throw away my Mounjaro pen after 30 days even if it has doses left?
Yes. After 30 days from first use, you must safely dispose of the pen in a sharps bin at your GP surgery or pharmacy, even if it contains unused doses. This is for safety reasons — the medication's stability cannot be assured beyond this timeframe.
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.