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
Should Mounjaro Be Kept In The Fridge?
Yes, Mounjaro KwikPen must be kept in the fridge before you start using it. Store unopened pens in a refrigerator at 2°C to 8°C in their original carton. Once you've used a pen for the first time, you can keep it at room temperature for up to 30 days. Never freeze Mounjaro — if a pen freezes, it cannot be used safely. Proper storage is essential to keep this prescription weight management injection effective and safe throughout your 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 Fridge Storage Rules (Before First Use)
Unopened Mounjaro pens must always be refrigerated:
- Store at 2°C to 8°C in a standard household fridge
- Keep in the original carton to protect from light
- Do not freeze — if frozen, the pen cannot be used
- Can be used until the expiry date printed on the carton if stored correctly
- Do not remove from the fridge until you are ready to use it
This tirzepatide injection is temperature-sensitive, which is why refrigeration is a UK prescription requirement. If you're unsure whether your pen has been frozen, contact your pharmacy or GP — they can advise whether it is still safe to use. Never use a pen that has been exposed to freezing temperatures.
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.
Room Temperature Storage (After First Injection)
After your first injection, you can store the pen at room temperature below 30°C for up to 30 days. This makes it easier to carry with you during the week between injections. Keep the pen away from direct sunlight and heat sources. After 30 days from first use, discard the pen safely even if there is still medication inside — do not continue using it. If you need guidance on safe needle disposal, ask your pharmacy or GP surgery; they can provide a sharps bin or collect used pens for you.
- 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 temperature should Mounjaro be stored at before use?
Unopened Mounjaro pens must be stored in a refrigerator at 2–8°C in their original carton. This is a prescription requirement in the UK. Keep away from the freezer compartment.
Can Mounjaro be kept at room temperature?
Yes, after your first injection, you can store the pen at room temperature (below 30°C) for up to 30 days. After 30 days, discard it safely.
What happens if Mounjaro freezes?
Do not use a frozen Mounjaro pen. Freezing damages the medication and makes it unsafe. If you think your pen has frozen, contact your pharmacy or GP for advice.
How long can unopened Mounjaro stay in the fridge?
Unopened pens can be kept refrigerated until the expiry date on the carton, provided they remain at 2–8°C in the original carton protected from light.
Is Mounjaro different from Wegovy for storage?
Yes. Mounjaro (tirzepatide) and Wegovy (semaglutide) are different medications. Mounjaro must be refrigerated before use; Wegovy also requires refrigeration before use but has slightly different room temperature timelines — always check your specific product guidance.
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.