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 Long Can You Store Mounjaro?
Mounjaro (tirzepatide) storage is straightforward once you understand the two key rules: refrigerated unopened pens last until their expiry date, and opened pens can be kept at room temperature for up to 30 days. This UK health guide explains exactly how to store your Mounjaro KwikPen safely, what happens if you freeze it, and how storage compares to Wegovy. Proper storage ensures your prescription medication remains effective for your weight management journey.
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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 Rules: Unopened vs Opened
Unopened Mounjaro KwikPens: Store in a refrigerator at 2°C to 8°C until the expiry date printed on the box. Keep pens in their original carton to protect from light. Do not freeze — if accidentally frozen, the pen must be discarded and not used.
Opened Mounjaro KwikPens: After your first injection, the pen can be stored at room temperature (below 30°C) for up to 30 days. This flexibility makes Mounjaro practical for daily life — you don't need to refrigerate between weekly doses. After 30 days, dispose of the pen safely even if it contains unused doses.
Why the difference? Once the pen is opened and exposed to air, the medication begins to degrade more quickly at colder temperatures. Room temperature storage is actually safer for opened pens during their active use period.
- Never reuse a pen after 30 days of opening
- Do not leave unopened pens out of the fridge for extended periods
- Check the expiry date before each injection
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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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Mounjaro vs Wegovy Storage: Practical Comparison
Both Mounjaro and Wegovy follow similar storage principles, but there are key differences. Wegovy (semaglutide) also requires refrigeration (2°C to 8°C) when unopened and can be kept at room temperature (below 30°C) for 30 days after first use. However, Mounjaro's KwikPen design offers slightly more user convenience.
The main practical difference: Mounjaro requires minimum 3 days (72 hours) between doses, while Wegovy has a 7-day fixed schedule. This means if you travel or miss a dose, Mounjaro storage flexibility can be particularly useful. Both medications degrade if exposed to extreme heat, direct sunlight, or freezing temperatures. Your GP or prescriber will provide specific guidance on your prescription, and storage instructions are also printed on each pen's packaging.
- 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 regular kitchen fridge?
Yes. A standard kitchen fridge between 2°C and 8°C is suitable for unopened Mounjaro KwikPens. Keep it in the original carton away from the back of the fridge where it's coldest. Once opened, you can move it to room temperature (below 30°C) for 30 days.
What if I accidentally freeze my Mounjaro pen?
Do not use a frozen pen. Freezing damages the medication and it will no longer be safe or effective. Discard it safely and contact your prescriber or pharmacy for a replacement. This is why it's important to avoid storing pens at the back of a freezer compartment.
How do I know if my Mounjaro has gone off?
Check the expiry date on the carton. If the pen has been opened, discard it after 30 days even if it looks clear. Do not use it if it appears discoloured, cloudy, or contains particles. When in doubt, ask your pharmacist before injecting.
Can I store Mounjaro in a travel coolbag?
Yes. A travel coolbag or insulated pouch with ice packs can keep unopened pens at 2°C to 8°C for short trips. Once opened, the pen doesn't need cooling for 30 days, making Mounjaro convenient for holidays. Avoid direct contact between ice packs and the pen.
What's the difference between Mounjaro's storage and Saxenda storage?
Saxenda (liraglutide) also requires refrigeration when unopened but is a daily injection, not weekly like Mounjaro. Mounjaro's once-weekly schedule and 30-day room temperature window after opening make storage slightly more flexible overall.
Ready to take control of your weight loss journey?
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