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
Can You Store Mounjaro At Room Temperature?
Yes, you can store Mounjaro at room temperature, but only after you've started using it. Once you've injected your first dose from a KwikPen, you can keep it at room temperature for up to 30 days. However, before first use, Mounjaro must be stored in a refrigerator between 2°C and 8°C. Understanding the correct storage requirements for your tirzepatide prescription is essential for maintaining the medication's effectiveness and safety.
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Calculate Your BMI Instantly
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.
Mounjaro Storage Temperature Guidelines
Before first use: Store unopened Mounjaro KwikPen pens in a refrigerator at 2°C to 8°C. Keep them in the original carton to protect from light and never freeze them — if your pen freezes, it cannot be used and must be discarded. You can safely use an unopened pen until the printed expiry date as long as it's been refrigerated continuously.
After first injection: Once you've used your first dose, you can store the pen at room temperature below 30°C for a maximum of 30 days. After 30 days, you must discard the pen, even if there are doses remaining. Keep it away from direct sunlight and heat sources. This flexibility makes Mounjaro convenient for travel or daily use — you don't need to carry a cooling bag after starting your dose.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Important Storage Safety Points
Never leave your Mounjaro pen in a car, direct sunlight, or near a heating source, as heat can damage the medication. If you're unsure whether your pen has been stored correctly — for example, if it's been left unrefrigerated for several hours before first use — contact your prescriber or pharmacist for guidance. When travelling, bring an insulated cooling bag with ice packs to keep unopened pens refrigerated until you're ready to use them. Check your pen for visible damage, cloudiness, or particles before injecting — if something looks wrong, don't use it and speak to your pharmacist. Proper storage ensures your tirzepatide works effectively at each dose in your dose titration schedule.
- 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 leave my unopened Mounjaro pen at room temperature overnight?
No. Unopened Mounjaro must remain refrigerated at 2°C to 8°C at all times until first use. Even one night at room temperature could affect the medication. Always keep unopened pens in the fridge. If this happens accidentally, contact your pharmacist for advice.
How long can I keep a started Mounjaro pen out of the fridge?
After your first injection, you can keep the KwikPen at room temperature (below 30°C) for up to 30 days. After 30 days, discard it. This 30-day window is from the date you first injected, not from when you opened the carton.
What should I do if my Mounjaro pen freezes?
Do not use a frozen pen. Freezing damages the medication and makes it unsafe to inject. Discard it and contact your prescriber or pharmacist about getting a replacement before your next scheduled injection.
Can I store Mounjaro in the bathroom?
Bathrooms are often warm and humid, which is not ideal. A cool kitchen cupboard is better for storing started pens at room temperature. Keep your pen away from steam, hot water, and direct heat.
Do I need a special cooler bag for travel with unopened Mounjaro?
Yes. When travelling with unopened pens, use an insulated bag with ice packs to keep them refrigerated at 2°C to 8°C. Once you start using a pen, you only need to keep it below 30°C, so a standard cool bag may be sufficient depending on your trip length.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.