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 to Store Mounjaro — UK Storage Guide
Storing your Mounjaro KwikPen correctly is essential for maintaining its effectiveness and safety. This prescription-only injection must be kept at specific temperatures to preserve the tirzepatide medication inside. Whether you've just collected your KwikPen from a pharmacy or you're managing your ongoing treatment, understanding proper storage conditions helps protect your medication and ensures each weekly injection remains as effective as intended. The storage rules differ depending on whether your pen is unopened or in use, so it's important to know both.
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Calculate Your BMI Instantly
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.
Unopened Mounjaro Storage — Refrigeration Requirements
Unopened Mounjaro KwikPen pens must be stored in a refrigerator at 2°C to 8°C — this is the cold zone of a standard household fridge, not the freezer compartment. Each KwikPen contains four weeks' worth of doses, and the refrigerator is where it should stay until you're ready to use it.
- Keep the pen in its original carton to protect it from light exposure
- Do not freeze Mounjaro — if it freezes accidentally, it cannot be used safely and must be discarded
- An unopened pen can be used until its printed expiry date, provided it has been kept refrigerated throughout
- If you need to transport your pen, use a cool bag with ice packs to maintain the correct temperature
- Check the expiry date on the carton before starting treatment
The original carton is your friend here — it's designed to protect the medication from light and helps you track the expiry date clearly.
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.
After First Use — Room Temperature Storage
Once you've used your first injection from a KwikPen, you can store it at room temperature (below 30°C) for up to 30 days. This gives you flexibility to keep your pen somewhere convenient like a kitchen cupboard or bathroom cabinet during the four weeks you're using it.
- Keep the pen away from direct heat and sunlight
- Do not refrigerate the pen once it has been opened and used
- Mark the start date on the carton so you know exactly when your 30 days ends
- After 30 days from first use, discard the pen safely — even if it looks like it has doses remaining
- Never return an opened pen to the fridge to extend its life
Room temperature storage is convenient, but the 30-day limit is absolute once the pen is in use.
- 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 my unopened Mounjaro pen in the freezer?
No. Freezing Mounjaro damages the medication and makes it unsafe to use. Always store unopened pens in the fridge at 2–8°C, not the freezer. If your pen has been accidentally frozen, do not use it — discard it safely and contact your prescriber or pharmacy.
How do I know when my 30-day room temperature storage ends?
Write the date you first used the pen on the carton when you inject your first dose. Count forward 30 days from that date — this is your expiry deadline. Many people mark it with a highlighter or permanent marker to avoid confusion.
What if I travel or go on holiday with my Mounjaro?
For short trips, use a cool bag with ice packs to keep an unopened pen at 2–8°C. If you're already using an opened pen, keep it below 30°C and away from heat and sunlight. For longer trips, plan ahead and ensure you'll have access to appropriate storage or consider collecting your next pen closer to your departure.
Can I reuse a Mounjaro pen once I've finished the four doses?
No. Each KwikPen is single-use and contains exactly four weekly injections. Once you've administered all four doses (or after 30 days from first use, whichever comes first), the pen must be discarded safely into a sharps bin or as directed by your pharmacist.
What should I do if my Mounjaro pen looks cloudy or discoloured?
Mounjaro should be clear and colourless. If your pen looks cloudy, frozen, discoloured, or contains particles, do not use it. Discard it safely and contact your pharmacy or prescriber — they can provide a replacement. Never use a damaged or unclear medication.
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.