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 Do I Store Mounjaro? Complete UK Storage Guide
Proper storage of your Mounjaro KwikPen is essential to maintain its effectiveness and safety. Whether you've just received your prescription or are already using tirzepatide as part of your weight management programme, understanding the correct storage conditions is crucial. This guide explains exactly how to store Mounjaro in the UK, from unopened pens to after your first injection, plus what to do if you've accidentally exposed your pen to the wrong temperature.
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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.
Mounjaro Storage Temperature and Refrigeration Rules
Unopened Mounjaro KwikPen pens must be stored in a refrigerator at 2°C to 8°C until you're ready to use them. Keep the pen in its original carton to protect it from light exposure. Mounjaro pens will remain safe to use until their printed expiry date as long as they stay refrigerated at the correct temperature.
- Do not freeze Mounjaro — if a pen has been frozen, do not use it under any circumstances
- Store away from heat sources and direct sunlight
- Keep the original carton intact for protection
- Check the expiry date before use
After your first injection, you can store the pen at room temperature below 30°C for up to 30 days. This flexibility makes it easier to carry your weekly injection with you. After 30 days from first use, you must dispose of the pen safely, even if there's remaining medication inside. This timing helps ensure the medication remains stable and safe. If you're receiving Mounjaro through an NHS specialist weight management service or via a private UK prescription, your pharmacist will provide detailed storage instructions with your pens.
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Access and Cost: NHS vs Private Routes in the UK
Access to Mounjaro (tirzepatide) in the UK differs depending on whether you're using the NHS or private route. NHS access is through specialist tier 3 or 4 weight management services following a GP referral, but availability varies significantly by region and waiting lists can be lengthy. Private access is faster — you'll complete an online clinical assessment with a UK-licensed prescriber, receive a prescription if clinically appropriate, and have your Mounjaro dispensed by a GPhC-registered pharmacy.
Private Mounjaro costs typically range from £130 to £300+ per month depending on your dose, as each KwikPen contains four weekly injections. Your prescriber will assess your eligibility based on your BMI, health conditions, and medical history. Try our GLP-1 weight loss calculator to explore how tirzepatide might support your weight management goals, and use our BMI calculator to check your eligibility threshold.
Storage at home is straightforward once you know the rules. Most people keep unopened pens in their home fridge near the back (coldest area), away from the door where temperature fluctuates. After your first injection, the same pen can travel with you in a bag at room temperature for up to 30 days. If you're travelling and need to keep your pen cool, a small cool bag without direct ice contact works well. If you accidentally leave your Mounjaro at room temperature before opening it, contact your pharmacist or prescriber for guidance — brief exposure (a few hours) is usually fine, but prolonged room temperature storage of unopened pens should be avoided. Always dispose of used or expired pens in a sharps bin or as directed by your pharmacist.
- 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 freezer?
No. Mounjaro must never be frozen. If your KwikPen has been frozen, do not use it — discard it safely and contact your pharmacist or prescriber for a replacement. Freezing damages the medication and makes it unsafe.
How long can Mounjaro stay out of the fridge after I start using it?
After your first injection, the same Mounjaro KwikPen can be kept at room temperature (below 30°C) for up to 30 days. After 30 days from first use, dispose of the pen safely, even if medication remains inside.
What do I do if I accidentally left my unopened Mounjaro at room temperature overnight?
Brief room temperature exposure is usually acceptable. Contact your pharmacist or prescriber for specific guidance, especially if it was left in a warm environment (above 25°C). They may advise you to use it or replace it depending on how long and how warm it was.
Can I travel with my Mounjaro KwikPen?
Yes. After first use, your Mounjaro can travel in a bag at room temperature for up to 30 days. For unopened pens, use a travel cool bag (without direct ice contact) to maintain 2–8°C. Always carry your prescription or documentation when travelling.
How should I dispose of my used Mounjaro KwikPen?
Used Mounjaro pens are sharps waste and should be disposed of in a sharps bin. Ask your pharmacist for a sharps bin if you don't have one, or take your used pen to a pharmacy — they'll dispose of it safely and legally.
Ready to take control of your weight loss journey?
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