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
Does Mounjaro Need to Be Refrigerated After Opening?
Yes, Mounjaro can be stored at room temperature after you first use it, but only for a limited time. Once you've opened your KwikPen, you have up to 30 days to use it at room temperature (below 30°C) before you must dispose of it. Understanding proper Mounjaro storage is crucial for keeping your tirzepatide injection safe and effective throughout your weight management treatment.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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 After Opening — Temperature and Timeline
After your first injection, Mounjaro can be stored in two ways:
- Room temperature (below 30°C) for up to 30 days
- Refrigerator at 2–8°C for the full expiry date if you prefer
Many UK patients keep their KwikPen at room temperature after opening for convenience, as long as it's within the 30-day window. However, if you prefer to return it to the fridge, you can do so at any point. Once 30 days have passed since first use, dispose of the pen even if it contains remaining doses — unused medication cannot be stored beyond this limit.
Keep your pen away from direct sunlight, heat sources, and freezing conditions. If your Mounjaro has been frozen, do not use it under any circumstances. When travelling or on holiday, keep your KwikPen in a cool bag or insulated pouch if room temperature storage will exceed the safe threshold.
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.
NHS Prescription vs Private Mounjaro — Storage and Access in the UK
Whether you obtain your Mounjaro through NHS specialist weight management services or via a UK private prescription, storage requirements are identical. NHS access is through tier 3/4 specialist services (often with long waiting lists), while private online consultations with UK-licensed prescribers offer faster access through GPhC-registered pharmacies.
Private Mounjaro typically costs between £129–£180 per month depending on your dose, with your KwikPen delivered directly to your home. All doses require the same careful storage management. Your prescriber or pharmacist will provide detailed storage and handling instructions with every delivery. Use our free GLP-1 weight loss calculator above to explore potential outcomes at different tirzepatide doses, and try the BMI calculator to track your progress alongside weight management treatment.
- 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 refrigerate Mounjaro again after opening?
Yes. Once opened, you can move your Mounjaro between room temperature and the fridge as often as you need during the 30-day window. There's no limit to how many times you switch storage locations, as long as you stay within the safe temperature ranges (2–8°C in the fridge, below 30°C at room temperature). However, always avoid freezing.
What happens if Mounjaro is left out overnight?
A single night at room temperature (below 30°C) will not damage your Mounjaro. Your 30-day clock starts from your first injection, so occasional room temperature exposure is normal and expected. If your pen has been left above 30°C for extended periods or in direct sunlight, contact your pharmacist before using it to confirm safety.
How do I know if my Mounjaro has been frozen?
Frozen Mounjaro may show visible ice crystals, cloudiness, or discolouration inside the pen. If you suspect freezing, do not use the pen — contact your pharmacist immediately. Always store your KwikPen in the main compartment of your fridge, never in the freezer section or on the back wall where it's coldest.
Can I travel with my opened Mounjaro KwikPen?
Yes. Keep your opened pen in an insulated cool bag or travel cooler case with ice packs if you'll be away for more than a few hours in warm weather. Room temperature exposure for travel (below 30°C) is acceptable within your 30-day window. Never pack it in checked luggage where it may freeze in the cargo hold — always keep it in your carry-on bag.
What's the difference between Mounjaro and Wegovy storage?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) have similar storage rules after opening: up to 30 days at room temperature below 30°C, or back in the fridge at 2–8°C. The main difference is injection frequency — Mounjaro is once weekly and Wegovy is also once weekly, so both follow the same 30-day disposal timeline from first use.
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.