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 to Store Mounjaro Safely — UK Storage Guide
Mounjaro (tirzepatide) is a prescription-only, once-weekly injection for weight management in UK adults. Proper storage is essential to keep your medication safe and effective. Your KwikPen contains a potent dual GIP and GLP-1 receptor agonist that requires careful handling. This guide explains exactly how to store unopened and opened Mounjaro pens, what temperatures to use, and when to dispose of your injection safely.
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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.
Storing Unopened Mounjaro Pens
Unopened Mounjaro KwikPen devices must be stored in a refrigerator between 2°C and 8°C. Keep your pens in their original carton to protect them from light exposure. Do not freeze your medication — if a pen has been frozen, do not use it under any circumstances. Unopened pens can be used until the printed expiry date on the carton, provided they have been stored correctly in the fridge the entire time.
- Store at 2–8°C in a standard fridge (not the freezer compartment)
- Keep pens in original carton for light protection
- Check the expiry date before use
- Never use a pen that has been frozen
- Store away from direct heat sources
If you are unsure about storage conditions at home, speak to your GP or the pharmacy that dispensed your Mounjaro.
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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.
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Storing Opened Mounjaro Pens and Disposal
Once you have used your first injection from a KwikPen, you can store the pen at room temperature (below 30°C) for up to 30 days. After 30 days from first use, you must dispose of the pen safely, even if medication remains. Never store an opened pen back in the refrigerator.
- Room temperature storage: below 30°C maximum
- Duration: up to 30 days from first injection only
- Keep away from heat and direct sunlight
- Dispose of after 30 days, even if partly full
- Use a sharps bin for safe needle disposal
Your GP surgery or local pharmacy can provide a sharps bin and disposal advice if needed. Never throw Mounjaro pens in regular household waste.
- 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 in the door of my fridge?
Yes, the fridge door is acceptable if it maintains a temperature of 2–8°C. However, fridge doors experience more temperature fluctuation than the main compartment. If your door temperature varies significantly, store unopened pens in the main body of the fridge instead.
What should I do if my Mounjaro pen has been left out of the fridge?
If an unopened pen has been left at room temperature for less than 24 hours, it may still be safe — check the carton for specific guidance. If it has been left out longer, or if you are unsure, contact your pharmacist or GP before using it.
Can I travel with my Mounjaro across the UK?
Yes. Use a cool bag or insulated travel case with ice packs to maintain 2–8°C during travel. Keep the pen in its carton. If travelling by plane, inform security as it is a medical device. Never pack Mounjaro in checked luggage where temperatures cannot be controlled.
How do I dispose of my empty KwikPen safely?
Place used pens in a sharps bin (yellow needle disposal container). Your GP surgery, local pharmacy, or NHS walk-in centre will accept your sharps bin. Never dispose of pens in household waste or recycling bins.
Is Mounjaro the same as Wegovy for storage purposes?
No. Mounjaro (tirzepatide) and Wegovy (semaglutide) have different storage requirements. Both use once-weekly injections but have slightly different formulations. Always follow the specific storage instructions on your medication's carton, not general GLP-1 guidance.
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