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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How Long Can Mounjaro Be Kept At Room Temperature?
Mounjaro (tirzepatide) can be stored at room temperature for up to 30 days after you first use the KwikPen. Before first use, your pen must be kept in the refrigerator at 2°C to 8°C. Understanding proper storage is essential for maintaining the safety and effectiveness of this prescription-only weight management injection. Incorrect storage could damage the medication and make it unsafe to use. This guide covers UK storage rules for Mounjaro and what to do if your pen has been left out accidentally.
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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.
Mounjaro Storage Rules — Before and After First Use
Before first use: Store unopened Mounjaro KwikPens in the refrigerator at 2°C to 8°C. Keep the pen in its original carton to protect it from light. It can stay refrigerated until the expiry date printed on the carton.
After first use: Once you have used a dose, you may store the pen at room temperature (below 30°C) for up to 30 days. After 30 days, you must dispose of the pen safely, even if medication remains inside. Do not return it to the refrigerator after it has been kept at room temperature — keep it at room temperature for the full 30-day period.
Avoid heat and light: Whether refrigerated or at room temperature, keep Mounjaro away from direct sunlight, heat sources, and freezing conditions. Never freeze a KwikPen — if it has frozen, do not use it.
- Refrigerated (unopened): until expiry date
- Room temperature (after first use): up to 30 days maximum
- Never freeze or expose to extreme heat
- Always keep in original carton when refrigerated
Clinically BackedWeight Loss
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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.
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What If Mounjaro Has Been Left Out of the Fridge Accidentally?
If your unopened Mounjaro pen has been left at room temperature by accident, check how long it was unrefrigerated. If it was less than 30 days at room temperature, it may still be safe to use — return it to the refrigerator immediately and use it normally. However, if you are unsure how long it has been left out, or if it has been exposed to temperatures above 30°C or to direct sunlight, contact your prescriber or pharmacist for advice before using it.
Never use Mounjaro if it has been frozen, even if it has thawed. If your pen has been damaged, discoloured, or contains particles, do not use it. Always check the pen visually before each injection. If in doubt, ask your GP or the pharmacy that dispensed your prescription — they can advise whether it is safe to use or whether you need a replacement.
- 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 at room temperature before using it for the first time?
No. Unopened Mounjaro KwikPens must be stored in the refrigerator at 2°C to 8°C until first use. Only after you have taken your first dose can you store the pen at room temperature (below 30°C) for up to 30 days.
How many days exactly can I keep Mounjaro at room temperature after first use?
Up to 30 days. After 30 days, you must dispose of the pen safely, even if there is medication left inside. Do not return it to the refrigerator after it has been at room temperature.
What temperature counts as "room temperature" for Mounjaro storage?
Room temperature for Mounjaro is below 30°C. Avoid direct sunlight, heat sources, and areas with fluctuating temperatures. A kitchen cupboard away from the oven is typically suitable.
What should I do if my Mounjaro pen has been frozen?
Do not use it. Freezing damages tirzepatide and makes it unsafe. If your pen has been frozen, contact your prescriber or pharmacist for a replacement. Always protect Mounjaro from freezing conditions.
Can I extend the 30-day room temperature storage period by putting Mounjaro back in the fridge?
No. Once your KwikPen has been kept at room temperature, it must remain at room temperature for the full 30-day period — do not return it to the refrigerator. After 30 days, discard it safely.
Ready to take control of your weight loss journey?
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