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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Does Mounjaro Need To Be Kept In A Fridge?
Yes, unopened Mounjaro KwikPen injections must be stored in a refrigerator at 2°C to 8°C until first use. Once you start using a pen, you can keep it at room temperature (below 30°C) for up to 30 days. Proper storage is essential because tirzepatide can lose effectiveness if exposed to heat or freezing temperatures. This guide explains exactly how to store your Mounjaro UK prescription safely and what to do if storage goes wrong.
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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 refrigerated at 2°C to 8°C (typically your fridge's main shelf). Keep the pen in its original carton to protect it from light. Do not freeze — if a pen has been frozen, it cannot be used and must be disposed of safely. Unopened pens can be stored until their expiry date as long as they remain properly refrigerated.
After first injection: Once you've used a Mounjaro KwikPen for the first time, you can remove it from the fridge and store it at room temperature below 30°C for up to 30 days. Keep the pen away from direct sunlight and heat sources like radiators or windowsills. After 30 days of room temperature storage, the pen must be disposed of, even if it contains unused doses.
- Storage temperature range: 2–8°C unopened; below 30°C opened
- Duration at room temperature: maximum 30 days after first use
- Keep original carton to protect from light
- Never freeze or expose to temperatures below 2°C
Clinically BackedWeight Loss
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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.
NHS Mounjaro Prescriptions and Storage Guidance
If you've been prescribed Mounjaro through NHS specialist weight management services or via a UK-licensed prescriber, your pharmacy will supply the medication in a fridge-ready carton. When your prescription arrives, store it immediately in the fridge at home. The NHS recommends checking the temperature of your fridge regularly to ensure it stays in the correct range — many modern fridges have a built-in thermometer. If you're travelling within the UK and cannot access a fridge, ask your prescriber or pharmacist about alternative arrangements or short-term storage options. Never leave Mounjaro in a hot car or unrefrigerated environment for extended periods.
If you have questions about storage specific to your tirzepatide prescription, contact your prescriber, pharmacist, or the GPhC-registered pharmacy that dispensed your medication.
Use our free GLP-1 weight loss calculator to understand how Mounjaro may support your weight management goals when used alongside lifestyle changes. Our BMI calculator can also help you track your progress from baseline — proper medication storage ensures consistent, effective treatment throughout your weight loss journey.
- 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 I store unopened Mounjaro at?
Unopened Mounjaro KwikPen must be stored in a refrigerator at 2°C to 8°C. Keep it in the original carton to protect from light. Do not freeze it — if frozen, it cannot be used and must be safely disposed of by your pharmacy.
Can I keep Mounjaro at room temperature once I start using it?
Yes. After your first injection, you can store the KwikPen at room temperature below 30°C for up to 30 days. Keep it away from direct sunlight and heat. After 30 days, the pen must be disposed of, even if it has remaining doses.
What happens if my Mounjaro freezes?
If a Mounjaro pen is exposed to freezing temperatures (below 2°C), it cannot be used and should not be injected. The tirzepatide becomes inactive. Return it to your pharmacy for safe disposal and contact your prescriber about a replacement.
Do I need a special fridge or cool bag for Mounjaro?
No. A standard domestic fridge works perfectly for Mounjaro storage. If travelling, a cool bag with ice packs can maintain the correct temperature temporarily. Never store in a freezer compartment — use only the main fridge shelf.
What should I do if my Mounjaro has been left out of the fridge?
If unopened Mounjaro has been left at room temperature for a short time (under 24 hours), it can usually be safely returned to the fridge. If it's been left out longer or at high temperature, contact your pharmacy or prescriber for advice before using it.
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.