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
Should You Keep Mounjaro In The Fridge?
Yes, unopened Mounjaro KwikPen devices must be stored in a refrigerator at 2°C to 8°C. Once you start using a pen, you can keep it at room temperature below 30°C for up to 30 days before disposal. Proper storage of your tirzepatide prescription is essential to maintain its effectiveness and safety. This guide explains UK storage requirements for Mounjaro and what happens if your pen gets too warm or frozen.
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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 Requirements
Unopened Mounjaro pens must always be refrigerated. Store unused KwikPen devices in a standard fridge at 2°C to 8°C — the temperature range of a typical household refrigerator. Keep the pens in their original carton to protect them from light exposure, which can damage the medication. Never freeze Mounjaro; if a pen has been frozen, it cannot be used safely and must be disposed of. Check the expiry date on your carton — unopened pens can be stored until this date if kept properly refrigerated. Each KwikPen contains four weekly doses, so proper storage ensures all four injections remain safe to use. If you're unsure whether your pen has been exposed to inappropriate temperatures, contact your prescriber or pharmacist before using it.
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.
After You Start Using Mounjaro
Once you use your first injection from a KwikPen, the storage rules change. You can now keep the pen at room temperature below 30°C for up to 30 days. This makes it easier to carry your pen with you during the day or store it in a kitchen cupboard rather than the fridge. However, do not store an in-use pen above 30°C or in direct sunlight, as heat will degrade the tirzepatide. After 30 days from first use, the pen must be safely disposed of — even if doses remain. Keep a note of when you first opened each pen so you know when to replace it. Always store your Mounjaro away from children and pets, and never share your pen with anyone else, even if they also take tirzepatide at the same dose.
- 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 happens if Mounjaro freezes?
If your KwikPen freezes, it cannot be used safely and must be discarded. Freezing damages the tirzepatide medication. Never try to thaw it or use a frozen pen. Contact your prescriber or pharmacist for advice on replacing it.
Can I travel with Mounjaro?
Yes. Pack unopened pens in a cool bag with ice packs during travel to keep them at 2–8°C. Once in use, you can carry your pen at room temperature below 30°C for up to 30 days, making travel easier than with some other medications.
What's the difference between storage and access for Mounjaro vs Wegovy?
Both Mounjaro and Wegovy require similar fridge storage when unopened (2–8°C) and can be kept at room temperature after starting (below 30°C for 30 days). Storage rules are identical — the main difference is the medication type and dosing schedule, not how you store them.
Do I need a prescription to buy Mounjaro in the UK?
Yes, Mounjaro is prescription-only in the UK. You can access it through NHS specialist weight management services or private online prescribing following a clinical assessment. Once prescribed, you'll receive instructions on storage and delivery from your pharmacy.
Can I store Mounjaro in a travel cooler instead of a fridge?
Yes, you can use a travel cooler or cool bag with ice packs to maintain 2–8°C for unopened pens during holidays or when away from home. Once in use, room temperature storage below 30°C is fine, so you don't need cooling during the day.
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.