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 Mounjaro Last In The Fridge?
Mounjaro (tirzepatide) storage is straightforward once you understand the key timelines. Unopened Mounjaro KwikPens can be stored in a refrigerator at 2–8°C until the expiry date printed on the box — typically around two years from manufacture. Once you've used your first injection from a pen, it can be stored at room temperature for up to 30 days. Understanding these storage rules is essential for keeping your prescription weight loss medication safe and effective.
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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 Rules
Unopened Mounjaro pens must be stored in a fridge at 2–8°C (standard refrigerator temperature). Keep them in the original carton to protect from light. Unopened pens remain safe to use until the expiry date on the packaging — usually around two years. Never freeze Mounjaro; if it has been frozen, do not use it.
After first use, your Mounjaro pen can be stored at room temperature (below 30°C) for a maximum of 30 days. Once 30 days have passed since first use, the pen must be disposed of, even if it contains remaining doses. Store at room temperature away from direct sunlight and heat sources like radiators or windowsills. This is important because the medication's stability changes once the pen has been in use.
Each Mounjaro KwikPen contains four weekly doses. If you're on a higher dose during titration, always check your specific pen's expiry date after opening.
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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.
Mounjaro vs Wegovy Storage Comparison
Unlike Mounjaro, Wegovy (semaglutide) has slightly different storage requirements. Unopened Wegovy pens also require 2–8°C refrigeration until expiry, but opened pens can only be stored at room temperature for 28 days — shorter than Mounjaro's 30-day window. Both medications use once-weekly KwikPen delivery systems, but the dose titration schedules differ. Mounjaro starts at 2.5 mg and can escalate to 15 mg maximum, whilst Wegovy begins at 0.25 mg up to 2.4 mg. Your GP or prescriber will recommend which medication suits your eligibility and health profile through a clinical assessment.
Try our GLP-1 weight loss calculator to explore potential results with either medication alongside lifestyle changes.
- 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 store Mounjaro in a standard home fridge?
Yes. Standard home fridges maintain 2–8°C, which is perfect for unopened Mounjaro pens. Keep them in the original carton to block light. Do not store Mounjaro in the freezer compartment.
What happens if Mounjaro freezes?
If Mounjaro freezes, the medication becomes unsafe and should not be used. Discard the frozen pen and contact your pharmacy for a replacement immediately.
How long after opening can I use a Mounjaro pen?
After your first injection from a pen, you have 30 days to use the remaining three doses at room temperature. After 30 days, dispose of the pen even if doses remain.
Can I travel with Mounjaro?
Yes, but with care. Unopened pens must stay refrigerated during travel using a cool bag with ice packs (keeping temperature 2–8°C). Once opened, you can carry your pen at room temperature for up to 30 days, making it travel-friendly during your injection schedule.
What's the difference between Mounjaro and Wegovy storage?
Both require 2–8°C refrigeration unopened. Once opened, Mounjaro lasts 30 days at room temperature, whilst Wegovy lasts 28 days. Both must be kept in original packaging and away from light and heat.
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.