The UK's most complete GLP-1 guide
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- 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 Store Mounjaro — Complete UK Storage Guide
Mounjaro (tirzepatide) requires careful storage to remain safe and effective. Whether you've just started your prescription or are switching from Wegovy, understanding proper storage conditions is essential for getting the most from your weight management treatment. This guide covers unopened and opened KwikPen storage, temperature requirements, and how Mounjaro storage compares to other GLP-1 medications available in the UK.
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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 — Unopened and Opened Pens
Unopened Mounjaro pens must be stored in a refrigerator at 2°C to 8°C — the same temperature as standard household fridges. Keep pens in their original carton to protect them from light exposure. Unopened pens can remain stored this way until the expiry date printed on the packaging. Never freeze Mounjaro, as freezing damages the medication and makes it unsafe to use.
After first use, Mounjaro can be stored at room temperature below 30°C for up to 30 days. This allows flexibility if you're travelling or don't have consistent fridge access. Once 30 days have passed since first opening a pen, discard it safely even if medication remains — the formulation becomes unstable. Each Mounjaro KwikPen contains four weeks' worth of doses (one injection per week), so storage planning is straightforward if you follow your injection schedule consistently.
- Store unopened: 2°C to 8°C in original carton
- Store opened: below 30°C for up to 30 days
- Never freeze — freezing makes it unsafe
- Discard 30 days after first use regardless of remaining doses
- Keep away from direct heat and sunlight
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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.
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Mounjaro vs Wegovy — Storage Comparison
Both Mounjaro and Wegovy are once-weekly injectable GLP-1-based medications, but their storage requirements differ slightly. Wegovy (semaglutide) also requires refrigeration at 2°C to 8°C when unopened and can be stored below 30°C for up to 30 days after opening — identical to Mounjaro. The key difference is the mechanism: Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1 receptor agonist only. Clinical trials showed Mounjaro helped participants lose an average of 15–21% body weight, while Wegovy supported approximately 15% average weight loss in the STEP-1 trial. Individual results vary significantly, and your prescriber will assess which medication suits your health profile during your clinical assessment. Storage conditions are equally straightforward for both, making either suitable for UK patients managing their storage at home.
- 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 the freezer?
No. Freezing Mounjaro damages the medication and makes it unsafe to use. Always store unopened pens in a standard fridge at 2°C to 8°C, never in the freezer compartment.
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, discard the pen safely even if medication remains, as the formulation becomes unstable.
Do I need to store Mounjaro in the original carton?
Yes. Keep unopened Mounjaro pens in the original carton to protect them from light exposure. This helps maintain the medication's stability until you're ready to use it.
What's the difference between storing Mounjaro and Wegovy?
Storage requirements are nearly identical — both require 2°C to 8°C when unopened and can be stored below 30°C for up to 30 days after opening. Both must be discarded 30 days after first use.
Can I travel with Mounjaro that's been opened?
Yes. Opened Mounjaro can be stored below 30°C for up to 30 days, making it suitable for short trips. Use an insulated bag if travelling and keep it away from direct heat and sunlight.
Ready to take control of your weight loss journey?
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