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
Mounjaro Storage Temperature — UK Guidelines
Storing your Mounjaro (tirzepatide) KwikPen correctly is essential for maintaining its effectiveness and safety. In the UK, whether you've received your prescription through NHS specialist services or a private prescriber, proper storage ensures your weight management medication remains potent until you use it. Understanding the temperature requirements—both before and after opening—helps prevent waste and ensures optimal results when taken alongside reduced-calorie diet and physical activity changes.
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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 First Use
Unopened Mounjaro pens must be stored in a refrigerator at 2°C to 8°C (standard fridge temperature). Keep pens in their original carton to protect them from light damage. Do not freeze your Mounjaro—if a pen has been frozen, it should not be used. Unopened pens can be kept in the fridge until the expiry date printed on the carton without losing effectiveness.
After you open your first pen, you can switch to room temperature storage (below 30°C) for up to 30 days. Once 30 days have passed since first use, dispose of the pen safely in a sharps bin. This applies even if there is still medication remaining in the pen. Room temperature storage makes it easier to travel or keep your pen accessible during your 4-week dose cycle, but always keep it away from direct heat, sunlight, and radiators.
Never store Mounjaro in a freezer compartment or allow it to freeze, as this damages the medication. If you're unsure whether a pen has been frozen, ask your pharmacist or prescriber before using it.
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.
Storage Tips for UK Users — Practical Guidance
If you travel within the UK or abroad, you can carry your Mounjaro KwikPen at room temperature for short trips, but return it to the fridge as soon as you're home. A small portable cool bag or insulin travel case can help maintain safe temperatures during journeys. Always pack your pens in your hand luggage on flights—never in checked baggage, where freezing temperatures in the cargo hold could damage them.
Keep a written record of when you first opened each pen to avoid accidentally using it beyond the 30-day window. Your GP or prescriber can advise on safe disposal of used pens; they should go in a sharps container, not household waste. If you receive multiple pens as part of your tirzepatide treatment plan, stagger opening them to ensure you're using medication within the correct timeframe, particularly during dose titration phases.
- 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 fridge door?
Yes, the fridge door is suitable if it maintains 2°C to 8°C, though the main shelf is more stable. Avoid opening the fridge excessively, as this causes temperature fluctuations. The important thing is keeping it within the safe range without freezing.
What happens if Mounjaro freezes?
Frozen tirzepatide is damaged and should not be used. Freezing damages the active ingredient. If you suspect your pen has frozen, do not inject it—contact your pharmacist or NHS prescriber for advice on replacement.
How long can Mounjaro stay out of the fridge after first use?
Up to 30 days at room temperature (below 30°C). Once 30 days have passed since first opening, dispose of the pen safely in a sharps bin, even if medication remains. This ensures you're using fresh, effective medication.
Can I use Mounjaro if the expiry date has passed?
No. Always check the expiry date on the carton before using. Expired medication should be disposed of safely. Your pharmacist can advise on safe disposal methods for unused or expired Mounjaro pens.
Is Mounjaro storage different to Wegovy?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) follow the same storage rules: refrigerate unopened at 2–8°C, room temperature after opening for up to 30 days. However, Wegovy uses a different pen device, so always follow the specific instructions for your 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.