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- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
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- FAQs answered
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Mounjaro Temperature Storage vs Wegovy — How to Store Correctly
If you're prescribed Mounjaro (tirzepatide) or Wegovy (semaglutide) in the UK, proper storage is essential to keep your medication safe and effective. Both are prescription-only injectable weight loss treatments, but they have different storage requirements. Understanding the correct temperature, how long you can keep them at room temperature, and what to do if they've been exposed to heat or cold will help you get the most from your treatment. This guide compares storage requirements for both medications to help you store your KwikPen or auto-injection pen safely.
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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).
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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 vs Wegovy Storage Requirements — Side-by-Side Comparison
Mounjaro (tirzepatide) comes in a pre-filled KwikPen device and requires careful temperature control. Unopened pens must be stored in a refrigerator at 2°C to 8°C and kept in the original carton to protect from light. Mounjaro must never be frozen — if it freezes, the pen should be discarded. Once you start using a Mounjaro pen, you can keep it at room temperature below 30°C for up to 30 days. After 30 days, dispose of the pen even if there's still medication remaining.
Wegovy (semaglutide) comes in a pre-filled auto-injection pen with similar but slightly different storage rules. Unopened Wegovy pens must also be refrigerated at 2°C to 8°C in the original carton, away from light and heat. After first use, Wegovy can be kept at room temperature up to 25°C for 56 days — significantly longer than Mounjaro's 30-day window. Like Mounjaro, Wegovy must never be frozen.
The key difference: Mounjaro's room temperature shelf-life is 30 days, while Wegovy's is 56 days. Both require refrigeration when not in active use, and both must be protected from light and extreme temperatures.
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Practical Storage Tips and What to Do if Temperature-Damaged
Store both Mounjaro and Wegovy in a dedicated medication section of your fridge — not in the freezer compartment or door, where temperatures fluctuate. Keep pens in their original packaging to minimise light exposure. If you're travelling, use an insulated cooling bag with ice packs to maintain the correct temperature. Never leave your pen in direct sunlight, on a windowsill, or in a hot car.
If your Mounjaro or Wegovy pen has been frozen or exposed to temperatures above 30°C for Mounjaro (or 25°C for Wegovy), do not use it. Speak to your prescriber or pharmacist about a replacement. Damaged medication may be ineffective and could potentially be harmful. Always keep your pens in a safe place away from children and pets, and check the expiry date before each injection. Use our GLP-1 weight loss calculator to track your progress while using either medication.
- 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 use Mounjaro if it's been in the fridge but the carton got wet?
Yes, as long as the actual pen device is dry and hasn't been frozen or exposed to extreme heat. The carton is just protective packaging. However, if water has entered the pen mechanism itself, do not use it. Contact your prescriber or pharmacist for a replacement to be safe.
How long can I travel with Mounjaro or Wegovy without refrigeration?
Mounjaro can stay at room temperature (below 30°C) for up to 30 days. Wegovy can stay at room temperature (below 25°C) for up to 56 days. For flights or journeys, use an insulated cooling bag with ice packs to keep pens refrigerated throughout travel.
What's the difference between Mounjaro's 30-day room temperature shelf-life and Wegovy's 56 days?
Both medications have different formulations and stability profiles. Mounjaro (tirzepatide) requires return to refrigeration after 30 days at room temperature. Wegovy (semaglutide) can safely remain at room temperature for up to 56 days. Always check your medication leaflet for specific guidance.
If I accidentally left my Mounjaro pen out overnight at 20°C, is it still safe to use?
A single night at normal room temperature (below 30°C) is unlikely to damage Mounjaro. However, repeated exposure to warm temperatures or leaving it out continuously can degrade the medication. If in doubt, contact your prescriber or pharmacist before using the pen.
Does Mounjaro need to be kept in the original carton once it's been opened?
The carton is mainly protective during storage and transport. Once you're actively using the pen, you don't need the carton for the pen itself, but store the pen in a cool, dark place below 30°C. Keep unopened backup pens in the original carton in the fridge for protection.
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