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
Should You Keep Mounjaro in the Fridge?
Yes, Mounjaro (tirzepatide) must be kept in the fridge before you start using it. Unopened KwikPen devices need to be stored at 2°C to 8°C to maintain their effectiveness. However, once you begin treatment, the rules change slightly — your current pen can be kept at room temperature for up to 30 days. Understanding correct storage is essential for ensuring your prescription weight management medication works as intended. This UK health guide explains the exact storage requirements and what to do if you accidentally freeze your Mounjaro pen.
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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 Requirements Before and After Use
Unopened Mounjaro pens must always be stored in a refrigerator between 2°C and 8°C. Keep the pens in their original carton to protect them from light damage. Do not freeze Mounjaro — if a pen has been frozen, it cannot be used and should be disposed of safely. Most UK pharmacies will dispense Mounjaro in a cool bag with ice packs, and you should transfer it to the fridge as soon as you arrive home.
Once you have used your first injection from a KwikPen, the pen can be stored at room temperature (below 30°C) for the remaining 3 doses. Keep it away from direct sunlight and heat sources like radiators or windowsills. Each KwikPen contains 4 weekly doses, so after your first injection, you can keep that pen out of the fridge for up to 30 days. After 30 days from first use, the pen must be disposed of even if doses remain.
- Unopened pens: refrigerator (2–8°C) in original carton
- In-use pen: room temperature (below 30°C) for 30 days maximum
- Never freeze — frozen pens cannot be used
- Protect from direct sunlight and heat
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.
What Happens If You Accidentally Freeze Mounjaro?
If your Mounjaro pen has been frozen, do not use it. Freezing damages the medication and it will no longer work effectively. Check your pen for ice crystals or unusual appearance — if you suspect freezing has occurred, contact your pharmacy or prescriber immediately for advice. You may be entitled to a replacement pen depending on your prescription source (NHS or private). Always store unopened pens in the main fridge compartment, not the freezer, even if space is limited. If you're travelling or moving house, use an insulated cool bag with ice packs to keep pens at the correct temperature during transit.
When storing in-use pens at room temperature, do not leave them in cars, direct sunlight, or warm environments. Use our free GLP-1 weight loss calculator to track your projected results — consistent storage and adherence to your injection schedule will help you achieve the best outcomes alongside diet and physical activity changes.
- 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 keep my Mounjaro pen in the fridge door?
It's not ideal. Fridge doors experience temperature fluctuations each time they open. Store unopened Mounjaro pens in the main fridge compartment at 2–8°C. Once you've started using a pen, room temperature storage (below 30°C) is acceptable for up to 30 days.
How long can Mounjaro stay out of the fridge once I've started using it?
An in-use Mounjaro KwikPen can be stored at room temperature (below 30°C) for up to 30 days after your first injection. After 30 days, the pen must be disposed of safely, even if doses remain.
What should I do if my Mounjaro arrives warm in the post?
Contact your pharmacy immediately. If the pen has been kept above 30°C or shows signs of damage, request a replacement. Do not use a pen that may have been exposed to unsuitable temperatures. Always ask for insulated packaging and tracking.
Is Mounjaro the same as Wegovy for storage purposes?
No. Mounjaro (tirzepatide) and Wegovy (semaglutide) have different storage requirements. Wegovy pens also require refrigeration before use, but check your specific prescription's storage instructions. Your prescriber or pharmacist can clarify the exact rules for your medication.
Can I travel with my Mounjaro pen?
Yes. Use an insulated cool bag with ice packs to keep unopened pens at 2–8°C during travel. Once in-use, your pen can stay at room temperature (below 30°C) for up to 30 days, making it suitable for short trips without cooling equipment. ```
Ready to take control of your weight loss journey?
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