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
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How to Refrigerate and Store Mounjaro Safely
Mounjaro (tirzepatide) is a prescription-only weight management injection that requires proper storage to remain effective. In the UK, correct refrigeration is essential before you start using your KwikPen, and storage rules change once you've opened it. This guide explains exactly how to store your Mounjaro safely, what temperatures to use, and what to do if you've accidentally frozen or damaged your pens.
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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 Before First Use
Unopened Mounjaro KwikPens must be stored in a refrigerator between 2°C and 8°C (standard fridge temperature). Keep pens in their original carton to protect them from light exposure. Do not freeze your Mounjaro — if a pen has been frozen, it cannot be used and should be disposed of safely. Your pens are stable in the fridge until the expiry date printed on the carton, so you can store them well in advance of starting treatment.
- Store in the main fridge compartment, not the freezer
- Keep in original carton for light protection
- Check the expiry date before use
- Never expose to heat or direct sunlight
- If you're unsure about storage, ask your prescriber or pharmacist
When you receive your Mounjaro prescription from a UK pharmacy, the pens will arrive refrigerated. Transfer them to your home fridge immediately upon delivery.
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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.
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Storage After Opening Your First KwikPen
Once you've used your first Mounjaro injection, storage rules change. The opened KwikPen can now be stored at room temperature below 30°C for up to 30 days. You do not need to keep it in the fridge after first use, though refrigeration is still safe if you prefer. After 30 days from first use, the pen must be disposed of — even if it contains remaining doses.
- Room temperature storage: below 30°C maximum
- Valid for 30 days from first injection only
- Keep away from heat and sunlight
- Dispose safely after 30 days (ask your pharmacist how)
- Do not store in a car or warm environment
- 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 I accidentally freeze my Mounjaro?
If your unopened KwikPen has been frozen, it cannot be used and must be discarded. Freezing damages the medication and makes it unsafe. Always store unopened pens in the fridge compartment, never the freezer. Contact your prescriber or pharmacist if this happens — they can arrange a replacement.
Can I store my Mounjaro in the freezer to make it last longer?
No. Freezing Mounjaro damages the active ingredient (tirzepatide) and renders it unusable. Always store unopened pens at standard fridge temperature (2°C to 8°C) and opened pens at room temperature (below 30°C). Never attempt to extend shelf life by freezing.
How long can I keep an opened Mounjaro KwikPen at room temperature?
After your first injection, an opened KwikPen can be stored at room temperature below 30°C for exactly 30 days. After 30 days, the pen must be disposed of safely, regardless of whether doses remain inside.
What's the best way to transport Mounjaro if I'm travelling in the UK?
If travelling with unopened pens, use an insulated cool bag with ice packs to maintain 2°C to 8°C. For opened pens (within 30 days of first use), room temperature storage is fine if the journey is short. Never leave pens in a hot car or direct sunlight. Your prescriber can advise on travel storage.
Do I need a special fridge for Mounjaro storage?
No. A standard domestic fridge is fine — Mounjaro doesn't need a medical-grade refrigerator. Just ensure it maintains 2°C to 8°C and keep pens in their original carton. If your fridge temperature fluctuates, ask your pharmacist for advice on safe storage solutions.
Ready to take control of your weight loss journey?
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