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 Does Mounjaro Last Out Of The Fridge?
Mounjaro (tirzepatide) can be stored out of the fridge for a maximum of 30 days at room temperature after you first use it. Once opened, each KwikPen must be kept below 30°C and disposed of after 30 days, even if it still contains medication. Understanding proper storage is essential to keep your prescription medication effective and safe. Unopened pens must stay refrigerated at 2–8°C until you're ready to use them.
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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 — What You Need To Know
After first use, Mounjaro can be stored at room temperature (below 30°C) for up to 30 days. This means once you inject your first dose from a KwikPen, you have 30 days to use the remaining doses before it must be discarded. Keep it away from direct sunlight, heat sources, and extreme temperatures. Do not store it in a bathroom (moisture and temperature fluctuations) or near radiators. If you travel, a small insulated pouch can help maintain a stable temperature without refrigeration. Once the 30-day window closes, dispose of the pen safely in a sharps bin — do not throw it in regular waste. Never try to extend the shelf life by returning it to the fridge after room temperature storage, as temperature fluctuations can damage the medication.
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.
Freezing, Refrigeration, And Long-Term Access
Unopened Mounjaro pens must be stored in a refrigerator at 2–8°C. If a pen accidentally freezes, do not use it — frozen tirzepatide is no longer safe or effective. For long-term access, plan your prescription refills carefully. Each KwikPen contains 4 weeks' worth of injections (four once-weekly doses). If you're accessing Mounjaro privately through a UK online prescriber, discuss your prescription schedule to avoid gaps. NHS access through specialist services may involve longer waits between doses. Our GLP-1 weight loss calculator can help you track your dose progression and planned refill dates.
- 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 left out overnight?
If unopened, return it to the fridge immediately — it should still be safe if kept below 30°C. If it's already been opened and used, it's fine left out overnight once per day is acceptable during the 30-day window. However, consistent room temperature storage is only assured for the full 30 days if kept below 30°C. When in doubt, contact your prescriber.
What's the difference between Mounjaro and Wegovy storage?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) follow similar storage rules: refrigerate unopened pens at 2–8°C, then 30 days at room temperature after first use. Wegovy comes in a different pen device but has identical storage requirements. Check your specific medication's instructions, as individual products may vary slightly.
Can I travel with Mounjaro without a fridge?
Yes, for trips up to 30 days. Once you've opened a pen, you can carry it in an insulated travel pouch or cooling bag below 30°C. For longer trips, consider planning your dose schedule to align with your trip or ask your prescriber about alternative arrangements. Always carry your prescription documentation when traveling with medication.
What happens if Mounjaro gets too warm?
Exposure to temperatures above 30°C may reduce its effectiveness. If you suspect overheating, contact your prescriber or pharmacist — they can advise whether the pen is still safe to use. Never use medication that's been exposed to extreme heat, freezing, or direct sunlight for extended periods.
How do I know when my Mounjaro pen expires?
Each pen has an expiry date printed on the label. Once you open a pen, you have 30 days to use all four doses. Write the opening date on your pen with a marker to track the 30-day deadline. After 30 days, dispose of it safely in a sharps bin, even if there's medication remaining.
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.