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 I Refrigerate Mounjaro After Room Temperature?
No, you cannot refrigerate Mounjaro after it has been stored at room temperature. Once your tirzepatide KwikPen leaves the refrigerator and reaches room temperature, it enters a 30-day window during which it must be kept at room temperature — refrigerating it after this point can damage the medication and make it unsafe to use. Understanding Mounjaro storage rules is essential for keeping your prescription-only injection safe and effective throughout your weight management treatment.
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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 Storage Rules — What You Need to Know
Mounjaro must follow strict storage rules to remain safe and effective:
- Unopened pens: Store in a refrigerator at 2°C to 8°C until use. Keep in the original carton to protect from light. Unopened pens can be used until the expiry date printed on the box if kept refrigerated continuously.
- After first use: Once you use your tirzepatide KwikPen, it can be stored at room temperature (below 30°C) for up to 30 days only. After 30 days, you must dispose of the pen — even if medication remains inside.
- Do not re-refrigerate: If a pen has been at room temperature, returning it to the fridge can cause crystallisation or damage to the tirzepatide formula, making it unsafe.
- Never freeze: Frozen Mounjaro cannot be used and should be discarded.
Each KwikPen contains 4 doses (one month supply), so once you start using it, you are entering the 30-day room temperature window.
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.
Practical Storage Tips for Your Mounjaro KwikPen
Plan ahead to manage your Mounjaro storage effectively. If you use your pen on a Monday, mark day 30 on your calendar — that's your disposal deadline. Keep your pen in a cool place away from direct sunlight and heat sources, but do not place it back in the fridge. If you live somewhere very hot or travel frequently, ask your prescriber or pharmacist for advice on maintaining temperatures below 30°C. Our GLP-1 weight loss calculator can help you plan your dosing schedule, and your pharmacist can clarify any storage questions specific to your situation. Always check that your pen has not been frozen or exposed to extreme temperatures before using it — if you're unsure, contact your pharmacy.
- 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 happens if I refrigerate Mounjaro after using it at room temperature?
Refrigerating a Mounjaro pen after it has been at room temperature can damage the tirzepatide medication, potentially making it unsafe or ineffective. Once a pen enters the 30-day room temperature window, it should remain at room temperature throughout. If this happens by accident, contact your pharmacy or prescriber for guidance — do not use the pen.
How long can Mounjaro stay at room temperature once I start using it?
Once you use your first dose from a Mounjaro KwikPen, the pen can be stored at room temperature (below 30°C) for up to 30 days only. After 30 days, it must be disposed of safely, even if medication remains. Each pen is designed to last 4 weeks at room temperature.
Can I keep an unopened Mounjaro pen at room temperature?
No. Unopened Mounjaro pens must be stored in the refrigerator at 2°C to 8°C until you are ready to use them. They can remain refrigerated until the expiry date printed on the box, but should never be stored at room temperature before first use.
What should I do if my Mounjaro pen freezes?
Do not use a frozen Mounjaro pen. Freezing damages the tirzepatide formula. Dispose of the pen safely and contact your pharmacy to request a replacement. Inform them how the pen froze so you can avoid this in future.
Is Mounjaro the only tirzepatide option available on UK prescription?
Yes, Mounjaro is the brand name for tirzepatide licensed for weight management in the UK. It is a prescription-only medicine and the dual GIP/GLP-1 receptor agonist option. Your GP or prescriber can discuss whether this medication is suitable for you through NHS specialist services or private 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.