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
Do I Need To Keep Mounjaro In The Fridge?
Yes, unopened Mounjaro KwikPen devices must be stored in a refrigerator at 2–8°C and kept in their original carton to protect from light. However, once you start using a pen, you can keep it at room temperature (below 30°C) for up to 30 days. Understanding the correct storage requirements for your tirzepatide injections is essential to maintain their effectiveness and safety. Both Mounjaro and Wegovy have specific storage instructions, though their requirements differ slightly. This guide covers everything you need to know about keeping your Mounjaro safe and ready to use.
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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 — Full Details
Unopened Mounjaro pens: Store in a refrigerator between 2°C and 8°C. Keep in the original carton to protect from light exposure, as this protects the medication's stability. Do not freeze your pens — if accidentally frozen, the pen cannot be used and should be safely disposed of. Each KwikPen contains four weekly doses, so proper refrigeration of unopened pens is crucial before you start treatment.
- Temperature: 2–8°C (standard fridge temperature)
- Location: Keep in original carton on a shelf, not the door where temperature fluctuates
- Do not freeze — frozen pens must be discarded
- Check the expiry date before use
After first use: Once you inject your first dose, the pen can be stored at room temperature below 30°C for exactly 30 days. After 30 days from first use, the pen must be disposed of safely, even if it still contains medication. This is important for safety and efficacy.
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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
While both Mounjaro (tirzepatide) and Wegovy (semaglutide) are GLP-1 weight management injections available on UK prescription, their storage requirements differ slightly. Wegovy pens also require refrigeration at 2–8°C when unopened, but have a shorter room-temperature window — only 30 days after first use, same as Mounjaro. Both medications are prescription-only and require a clinical assessment before being prescribed by a licensed UK prescriber.
The key similarity is that both must start in the fridge and can transition to room temperature for a limited period once opened. Your prescriber or pharmacist will provide specific storage instructions with your medication. If you're unsure about your particular pen's requirements, always consult the patient information leaflet or contact the pharmacy that dispensed your prescription.
- 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 keep my unopened Mounjaro pen in the fridge door?
No — avoid the fridge door where temperature fluctuates. Store unopened pens on a shelf inside the main fridge body at a consistent 2–8°C. Temperature changes can affect the medication's stability.
What happens if my Mounjaro freezes?
If your Mounjaro pen freezes, it cannot be used and must be safely disposed of. Do not attempt to use a frozen pen. Keep it away from the freezer compartment and only store in the main fridge section.
How long can I keep Mounjaro at room temperature after opening?
Exactly 30 days from the date of first injection. After 30 days, the pen must be disposed of safely, regardless of how much medication remains inside.
Do I need to refrigerate Mounjaro between injections?
Once you've opened your first pen, you can keep it at room temperature (below 30°C) for the full 30 days. You do not need to refrigerate it between weekly injections during this period.
How should I dispose of my used Mounjaro pen?
Never throw it in household waste. Use a sharps bin if available (ask your pharmacist for one), or return used pens to a pharmacy or GP practice that has a sharps disposal facility. This is safe and free in the UK.
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.