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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Mounjaro Room Temperature Storage — What You Need to Know
Mounjaro (tirzepatide) can be stored at room temperature for up to 30 days after you first use your KwikPen, making it convenient for daily life and travel. However, proper storage guidance is essential to keep your medication safe and effective. This guide explains UK storage rules, temperature limits, and what to do if your pen is exposed to heat or cold. Use our GLP-1 weight loss calculator to explore potential outcomes, and consult your GP or prescriber about any storage concerns specific to your treatment plan.
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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
Once your Mounjaro KwikPen is opened and you've taken your first injection, you can store it at room temperature (below 30°C) for up to 30 days. This is much more flexible than the strict refrigeration required before first use, allowing you to keep your pen at home, in your bag, or while travelling without needing a cold bag or portable cooler.
- Storage temperature: below 30°C (86°F) — standard room temperature
- Duration: up to 30 days from first injection
- After 30 days: discard the pen, even if medication remains
- Keep away from direct sunlight and heat sources (radiators, windowsills, car dashboards)
- Do not refrigerate once opened — return to fridge only if absolutely necessary before next use
Before first use, unopened Mounjaro pens must stay in the refrigerator at 2–8°C. Only after your first injection does the 30-day room temperature window apply. If your pen has been in the fridge and you remove it, you're starting the 30-day timer.
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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.
Mounjaro vs Wegovy — Storage Comparison and Prescriber Suitability
Both Mounjaro and Wegovy allow room temperature storage for similar periods after opening, but the medications work differently. Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is GLP-1 only. In clinical trials (SURMOUNT for Mounjaro, STEP for Wegovy), both supported weight loss averaging around 15–21% and 15% body weight respectively — though individual results vary significantly. Your prescriber will assess which medication suits your health profile, medical history, and weight management goals. Both require a clinical assessment before prescription and are taken once weekly. Try our free GLP-1 weight loss calculator to estimate potential outcomes, and discuss storage practicalities with your prescriber or pharmacist when starting treatment.
- 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 my opened Mounjaro pen in a hot car or warm environment?
No. Mounjaro must stay below 30°C. A hot car can exceed this easily. If your pen is accidentally exposed to heat above 30°C, contact your prescriber or pharmacist — do not use it. Always keep your pen in a cool bag or insulated pouch during travel, and never leave it in direct sunlight or near heat sources like radiators or kitchen worktops.
What happens if I refrigerate my Mounjaro after opening it?
You can refrigerate an opened pen if necessary — it won't damage the medication. However, once removed from the fridge, the 30-day room temperature storage timer restarts. For example, if you've used your pen for 10 days at room temperature, then refrigerate it for a week, you still have 20 days of room temperature storage remaining before you must discard it.
Can I use my Mounjaro pen after 30 days at room temperature?
No. After 30 days of room temperature storage (from your first injection), you must discard the pen. This applies even if medication remains inside. Mounjaro pens are designed to be used within this timeframe for safety and effectiveness. Always note the date you first inject on your pen so you know when the 30-day window closes.
How does Mounjaro storage compare to Wegovy storage?
Both Mounjaro and Wegovy can be stored at room temperature (below 30°C) for up to 30 days after opening. Unopened pens of both medications must be refrigerated at 2–8°C. The main practical difference is that Wegovy is a daily dose pen (with multiple smaller doses), while Mounjaro is a once-weekly pen. Storage rules are essentially identical.
What should I do if my Mounjaro pen freezes?
Do not use a frozen Mounjaro pen. If it freezes (for example, left in a freezer or exposed to very cold temperatures), contact your prescriber or pharmacist. Freezing can damage the medication. Before first use, unopened pens should never be frozen — they must stay at 2–8°C only. After opening, avoid cold storage (below 2°C) unless medically advised.
Ready to take control of your weight loss journey?
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