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
How Long Can Mounjaro Be Stored at Room Temperature?
Mounjaro (tirzepatide) can be stored at room temperature for up to 30 days after first use. Once you've used your KwikPen for the first time, you can keep it below 30°C without refrigeration, but you must dispose of it after 30 days — even if medication remains inside. Before first use, your Mounjaro pen must be kept in a refrigerator between 2°C and 8°C. Understanding correct storage is essential for maintaining the medication's effectiveness and safety.
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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.
Room Temperature Storage Rules for Mounjaro
After your first injection, you can remove your Mounjaro KwikPen from the fridge and store it at room temperature (below 30°C) for up to 30 days. This makes it convenient to carry with you or keep at your desk during the week. However, once 30 days have passed since first use, you must dispose of the pen — do not continue using it even if it contains remaining doses.
- Maximum room temperature storage: 30 days from first use
- Temperature limit: below 30°C (keep away from direct heat and sunlight)
- Do not store in a car on hot days or near radiators
- Keep the pen in its original carton for protection
- If you forget to use your pen on schedule, you can still use it within 30 days of first use
This flexibility means you don't need to carry your Mounjaro in a cool bag every day — standard room temperature storage works perfectly well for the treatment week.
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Before First Use: Refrigerator Storage Essential
Unopened Mounjaro pens must always be refrigerated before your first injection. Store at 2°C to 8°C in a standard fridge — never freeze. Keep pens in their original carton to protect from light exposure. You can use unopened pens until their expiry date as long as they've been refrigerated continuously. If a pen is accidentally frozen, do not use it. When you first start tirzepatide as part of your dose titration schedule, your prescriber will advise you on when to begin using your first pen and how to store it properly during your starting dose phase.
- Refrigerator temperature: 2°C to 8°C
- Do not freeze — if frozen, discard
- Keep in original carton
- Check expiry date before use
- 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 my car overnight if it's cool?
Only if it stays below 30°C. If outdoor temperatures are warm or your car heats up, do not leave Mounjaro unrefrigerated for more than brief periods. For overnight storage, use the fridge. Once you've used your pen, you have 30 days at room temperature, but storing unopened pens in a car is not reliable temperature control.
What happens if Mounjaro gets too warm before I use it?
If an unopened or partially used pen exceeds 30°C or is exposed to direct sunlight for extended periods, the medication may become less effective. If you're unsure about temperature exposure, contact your prescriber or pharmacist — they can advise whether the pen is still safe to use. When in doubt, it's safer to discard and request a replacement.
Do I need a cool bag to carry Mounjaro at room temperature after first use?
No. Once you've started using your pen, you can carry it in a regular bag or keep it in a drawer at room temperature for up to 30 days. A cool bag is not necessary unless your environment is exceptionally warm or you want extra peace of mind during summer travel.
Can I use my Mounjaro pen if it's been in the fridge but I've forgotten the exact date I opened it?
If you cannot clearly remember when you first used your pen, it's safest to assume it's been longer than 30 days. Always write the date you first use your KwikPen on the carton with a pen so you have a clear record. If uncertain, contact your pharmacist or prescriber — they can advise based on how full the pen is and when you obtained it.
Is Mounjaro storage different from Wegovy or other GLP-1 injections?
Each GLP-1 or GIP/GLP-1 medication has specific storage instructions. Mounjaro's room temperature storage window is 30 days after first use, whereas semaglutide (Wegovy) has similar guidance. Always follow the patient information leaflet included with your specific medication. When comparing Mounjaro vs Wegovy or switching medications, ask your prescriber about storage differences.
Ready to take control of your weight loss journey?
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