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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Do You Need to Keep Mounjaro in the Fridge?
Yes, unopened Mounjaro KwikPen devices must be stored in a refrigerator at 2°C to 8°C. Once you've started using a pen, you can keep it at room temperature below 30°C for up to 30 days. Understanding proper storage is essential to keep your medication effective. This guide compares Mounjaro and Wegovy storage requirements so you know exactly how to look after your injection pens in the UK.
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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.
Storage Requirements: Mounjaro vs Wegovy
Mounjaro (tirzepatide) storage rules are straightforward. Unopened pens must be refrigerated at 2°C to 8°C and kept in their original carton away from light. You can use them until the expiry date if stored this way. Once you've used your first injection from a pen, it can be moved to room temperature (below 30°C) and kept for up to 30 days before disposal. Never freeze Mounjaro — if it freezes, you must discard it.
Wegovy (semaglutide) follows similar guidance. Unopened pens are stored refrigerated at 2°C to 8°C in the original packaging. After first use, Wegovy can also be kept at room temperature below 25°C for up to 30 days. Like Mounjaro, freezing renders it unusable.
- Both medications require a prescription following clinical assessment
- Storage errors may reduce medication effectiveness
- Always check your patient information leaflet for specific guidance
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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.
Practical Storage Tips for UK Users
Store unopened pens on a shelf in your fridge rather than in the door, where temperature fluctuates. Keep them in the original carton to protect from light exposure. Once started, write the date on your pen so you know when the 30-day room temperature window ends. If you're travelling, a cool bag with ice packs can maintain the 2–8°C range for short periods. Never store Mounjaro or Wegovy with other medications that might be frozen. Your pharmacist can advise on travel storage if you'll be away longer than 30 days from your first injection.
- 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 accidentally freeze Mounjaro?
If Mounjaro freezes, it becomes ineffective and must be discarded. Do not use a thawed pen. Contact your prescriber or pharmacist if you've accidentally frozen your medication to arrange a replacement.
Can I keep Mounjaro in the door of my fridge?
No. The fridge door experiences temperature fluctuations when opened repeatedly. Store unopened pens on a shelf inside the fridge to maintain a stable 2–8°C temperature.
How long can Mounjaro stay out of the fridge after first use?
Up to 30 days at room temperature below 30°C. Mark the date on the pen when you first use it so you know when to discard it.
Is Wegovy storage different from Mounjaro storage?
Very similar, but Wegovy room temperature storage has a slightly lower limit (below 25°C vs 30°C for Mounjaro). Both require refrigeration before first use and must be discarded if frozen.
What should I do with expired or unused Mounjaro pens?
Take them to a pharmacy for safe disposal. Do not throw them in household waste. Your pharmacy will handle them according to UK medicines disposal guidelines.
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.