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
Where to Store Your Mounjaro Pen — UK Guidelines
Storing your Mounjaro KwikPen correctly is essential to keep the medication safe and effective. Unopened pens must be refrigerated between 2°C and 8°C until you're ready to use them. Once you've started using a pen, you can keep it at room temperature below 30°C for up to 30 days. If your pen freezes, it's no longer safe to use. Proper storage protects the tirzepatide inside from heat and light damage, ensuring each weekly injection works as intended.
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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 vs Wegovy Storage — Key Differences
Mounjaro (tirzepatide) and Wegovy (semaglutide) have similar but slightly different storage requirements. Both are GLP-1 type medications (Mounjaro is a dual GIP/GLP-1 agonist), delivered via once-weekly injections, and both require careful temperature control.
- Mounjaro: Store unopened at 2–8°C; after first use, room temperature (below 30°C) for up to 30 days
- Wegovy: Store unopened at 2–8°C; after first use, room temperature (below 25°C) for up to 30 days
Wegovy has a slightly lower room temperature threshold (25°C vs 30°C for Mounjaro), so if you're using Wegovy during hot weather, extra care is needed. Both medications should never be frozen. Check the patient information leaflet on your specific pen for exact guidance, as storage instructions apply equally whether you access your Mounjaro or Wegovy through NHS specialist services or private prescription in the UK.
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 and Travel Tips
Keep unopened Mounjaro pens in the main body of your fridge, not the door, where temperature fluctuates. Store in the original carton to protect from light. When travelling, use an insulated cool bag with ice packs for longer journeys. If you're away from a fridge, your pen can safely remain at room temperature for the full 30 days once opened—you don't need to refrigerate it again if it warms up briefly. Mark your calendar with the date you first use each pen so you know when the 30-day window closes. After 30 days, dispose of the pen safely in a sharps bin or return it to a pharmacy for disposal—never throw it in household rubbish.
- 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 freeze my Mounjaro pen if I'm going on holiday?
No. Freezing damages tirzepatide and renders the pen unsafe to use. If your pen has frozen, discard it and use a new one. Always keep unopened pens in the fridge body (2–8°C), not the freezer.
How long can Mounjaro stay out of the fridge once I've opened it?
Up to 30 days at room temperature below 30°C. You don't need to refrigerate it again once removed. Write the start date on the pen to track the 30-day window accurately.
Is Mounjaro storage the same as Wegovy storage?
Very similar, but Wegovy has a slightly lower room temperature limit (25°C vs 30°C for Mounjaro). Both require refrigeration when unopened and both must never be frozen. Check your specific patient information leaflet for exact details.
What's the difference between Mounjaro and Wegovy besides storage?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist; Wegovy (semaglutide) is GLP-1 only. Clinical trials show both support weight loss alongside diet and exercise. Individual suitability is assessed by your prescriber through a clinical assessment.
Can I use my Mounjaro pen if it's been stored above 30°C?
If the pen was unopened and briefly exposed to warmth (not frozen), it's usually safe. However, prolonged heat exposure can damage the medication. When in doubt, contact your prescriber or pharmacy. Never use a pen that's been frozen, even if it thaws.
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.