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
Can You Keep Mounjaro In The Fridge?
Yes, you must keep unopened Mounjaro KwikPen devices in a refrigerator at 2–8°C. This is essential for maintaining the stability and effectiveness of tirzepatide, the active ingredient in Mounjaro. Proper storage ensures your prescription weight loss medication works as intended when you're ready to use it. Understanding storage requirements is a crucial part of using this GLP-1 and GIP receptor agonist safely and effectively in the UK.
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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.
Mounjaro Refrigerator Storage Rules
Unopened Mounjaro pens must always be stored in a refrigerator at a temperature between 2°C and 8°C. Keep the pens in their original carton to protect them from light exposure. Do not freeze Mounjaro — if a pen has been frozen, it cannot be used and should be disposed of safely. Store your KwikPen away from the back of the fridge where temperature may drop below 2°C. Check the expiry date before use; unopened pens can be used until the printed expiry date if stored correctly in the fridge. When collecting your prescription from a GPhC-registered pharmacy, ask how it was transported and stored, and refrigerate it immediately upon arrival home.
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 After First Use
Once you've used your first injection from a Mounjaro KwikPen, storage rules change. The pen can then be stored at room temperature (below 30°C) for up to 30 days after the first use. Keep it away from heat sources and direct sunlight. You must dispose of the pen safely 30 days after first use, even if medication remains inside. If your prescription dose requires multiple pens over several weeks — for example, during dose titration from 2.5 mg to 5 mg to 7.5 mg — keep unopened pens in the fridge and remove only the one you need for the current week.
- 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.
What temperature should Mounjaro be stored at in the fridge?
Unopened Mounjaro must be stored between 2°C and 8°C in a refrigerator. Keep it in the original carton. Do not store at the very back of the fridge where it may freeze, as frozen Mounjaro cannot be used.
Can you use Mounjaro after it's been frozen?
No. If a Mounjaro pen has been frozen, it must be discarded and not used. Freezing damages the tirzepatide formulation. Always monitor the temperature of your fridge to prevent accidental freezing.
How long can Mounjaro be kept out of the fridge after first use?
Once you've taken your first injection, the pen can be stored at room temperature (below 30°C) for up to 30 days. After 30 days, the pen must be disposed of safely, regardless of remaining doses.
Do you need to refrigerate Mounjaro between doses?
Yes. Between weekly injections, keep your Mounjaro KwikPen in the fridge at 2–8°C in its original carton. Only remove it when you're ready to inject. Return it to the fridge immediately after use.
What should you do if Mounjaro has been left out of the fridge?
If an unopened pen has been left at room temperature, check how long it was out. If less than 30 days before first use, it may still be safe — contact your pharmacy or GP for guidance. If it was frozen, discard it. Always ask your pharmacy about proper transport and storage when collecting your prescription.
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.