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 Long Does Mounjaro Last In The Fridge?
Mounjaro (tirzepatide) storage is straightforward but important for maintaining medication effectiveness. Unopened KwikPen pens last until their expiry date when refrigerated at 2–8°C. Once you start using a pen, it can be stored at room temperature below 30°C for up to 30 days. Understanding proper storage ensures your prescription weight management medication remains effective throughout your treatment. This guide covers UK storage requirements and practical tips for managing your tirzepatide supply safely.
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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 — Unopened vs Open Pens
Unopened Mounjaro KwikPen pens: Store in a refrigerator between 2°C and 8°C. Keep pens in their original carton to protect from light. They remain effective until the expiry date printed on the packaging — typically 18–24 months from manufacture. Never freeze Mounjaro; if a pen is accidentally frozen, do not use it. Transport unopened pens in a cool bag with ice packs if travelling.
After first use: Once you have injected your first dose, the opened pen can be kept at room temperature (below 30°C) for up to 30 days. You do not need to refrigerate it after opening. Mark the date you first used the pen with a permanent marker so you remember when the 30-day window ends. After 30 days, even if there is medication remaining, dispose of the pen safely in a sharps bin.
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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.
Mounjaro vs Wegovy Storage — Key Differences
Both Mounjaro and Wegovy are once-weekly GLP-1 receptor medications, but storage differs slightly. Like Mounjaro, Wegovy (semaglutide) is refrigerated unopened and can be stored at room temperature for up to 30 days after first use. However, the dosing regimens differ: Mounjaro uses a dual GIP and GLP-1 mechanism with doses from 2.5 mg to 15 mg weekly, while Wegovy is a GLP-1-only medication escalating to a maximum of 2.4 mg. Clinical trial data from SURMOUNT and STEP studies shows both support weight loss when combined with lifestyle changes. Your prescriber will assess which is suitable for you based on individual health needs and clinical assessment.
- 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 you use Mounjaro after it's been refrigerated then left at room temperature?
Yes. Unopened Mounjaro can go between the fridge and room temperature multiple times during the 4-week period before first use. Once opened, keep it at room temperature (not back in the fridge) for up to 30 days. Never re-refrigerate an opened pen.
What happens if Mounjaro freezes?
Do not use a frozen Mounjaro pen. Freezing damages the medication. Always store unopened pens in a refrigerator set to 2–8°C, never in the freezer compartment. If accidentally frozen, dispose of it safely and contact your prescriber for a replacement.
How do you know when to throw away an opened Mounjaro pen?
Mark the date on the pen when you first use it. After 30 days from that date, dispose of it safely in a sharps bin, even if it appears to have medication remaining. Never use Mounjaro beyond 30 days after opening.
Can you travel with Mounjaro and keep it cool?
Yes. Use an insulated travel case or cool bag with ice packs for short journeys (under 48 hours). For flights, you can store Mounjaro in aeroplane cabin baggage — it does not need to remain refrigerated for short flights. Contact your airline for specific guidance on medical supplies.
Is storage for Mounjaro different from other weight loss injections like Wegovy?
Both Mounjaro and Wegovy follow similar storage: refrigerated unopened (2–8°C), room temperature after opening (below 30°C for 30 days). The main difference is their mechanism — Mounjaro is a dual GIP+GLP-1 agonist while Wegovy is GLP-1 only — but storage requirements are essentially the same.
Ready to take control of your weight loss journey?
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