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 Have To Store Mounjaro In The Fridge?
Yes, Mounjaro (tirzepatide) must be stored in the fridge before you first use it. However, once you start using your Mounjaro KwikPen, you can keep it at room temperature for up to 30 days. Understanding proper storage is essential to keep your prescription weight loss injection effective and safe. This guide covers UK storage requirements, temperature guidelines, and practical tips for managing your Mounjaro pens at home.
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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
Before first use: Keep your unopened Mounjaro KwikPen in the fridge at 2°C to 8°C. Store it in the original carton to protect from light. Do not freeze the pen — if it freezes, the medication is damaged and cannot be used. Unopened pens can be kept in the fridge until the expiry date printed on the carton.
- Temperature range: 2°C to 8°C (standard fridge temperature)
- Keep in original carton away from direct sunlight
- Never freeze — this destroys the medication
- Check expiry date before each injection
After first use: Once you inject your first dose from a Mounjaro pen, you can remove it from the fridge and store it at room temperature (below 30°C) for up to 30 days. After 30 days, you must discard the pen even if medication remains. Keep it away from direct heat and sunlight.
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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.
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Mounjaro vs Wegovy Storage — Key Differences
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are once-weekly GLP-1 injections used for weight management in the UK, but they have different storage requirements. Wegovy also requires refrigeration before first use (2°C to 8°C) and can be kept at room temperature after opening for up to 30 days — the same as Mounjaro. The main difference is in their mechanism: Mounjaro is a dual GIP and GLP-1 receptor agonist, whilst Wegovy is a GLP-1 agonist only. Both are prescription-only medicines requiring clinical assessment. Storage guidelines are essentially identical, so your choice between them would be determined by your prescriber based on your individual health profile and clinical suitability, not by storage convenience.
- 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 store Mounjaro at room temperature from day one?
No. Unopened Mounjaro pens must be stored in the fridge at 2°C to 8°C. Only after your first injection can you keep the pen at room temperature (below 30°C) for up to 30 days. Always keep unopened pens refrigerated until you're ready to use them.
What happens if Mounjaro freezes?
If your Mounjaro pen freezes, the medication is damaged and cannot be used safely. Do not use a frozen pen. Store your Mounjaro in a standard fridge compartment, not the freezer. If accidental freezing occurs, contact your pharmacist or prescriber for guidance on obtaining a replacement.
How long can I keep Mounjaro at room temperature after opening?
Once you inject your first dose, you can keep the Mounjaro pen at room temperature (below 30°C) for up to 30 days. After 30 days, the pen must be discarded even if there is medication remaining. Mark the start date on your pen to track the 30-day window.
Do I need to refrigerate Mounjaro between weekly injections?
After your first injection, you do not need to refrigerate Mounjaro between doses. Keep your in-use pen at room temperature away from direct heat and sunlight. Only unopened backup pens should be stored in the fridge until needed.
What temperature is safe for storing opened Mounjaro?
Store opened Mounjaro below 30°C (room temperature). Avoid hot environments, direct sunlight, and heat sources like radiators or car dashboards. A cool, dry cupboard away from bathroom steam is ideal. Do not refrigerate after opening — cold below 2°C can damage the pen.
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