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 Stored in the Fridge?
Yes, unopened Mounjaro KwikPen devices must be stored in a refrigerator at 2°C to 8°C to maintain effectiveness. Once you start using a pen, you can keep it at room temperature (below 30°C) for up to 30 days. Understanding proper storage is essential for anyone prescribed this weight management injection in the UK, as incorrect storage can damage the medication and affect how well it works alongside your reduced-calorie diet and increased physical activity.
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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 for Unopened and In-Use Mounjaro Pens
Unopened Mounjaro pens must be refrigerated:
- Store at 2°C to 8°C (standard fridge temperature)
- Keep in the original carton to protect from light
- Do not freeze — if a pen freezes, discard it and do not use
- Can be used until the printed expiry date if kept refrigerated
After starting a pen (once you've given your first injection):
- Can be stored at room temperature below 30°C
- Use within 30 days of first injection
- After 30 days, dispose of the pen safely even if medication remains
- Keep away from direct heat and sunlight
Each Mounjaro KwikPen contains 4 weekly doses. Proper storage ensures the tirzepatide remains effective throughout your dose titration schedule, whether you're starting at 2.5 mg or progressing to higher maintenance doses.
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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 and Safety Guidance
Keep a small notebook or phone reminder for your pen's 30-day "in-use" countdown after first use — this prevents accidental use of expired pens. Never store Mounjaro in the freezer compartment of your fridge, and avoid placing it near the back where it may be too cold. If you're travelling within the UK, insulated pen cases with temperature-control ice packs are available, though your prescribed pen should reach your home within a few days. Always check the pen's appearance before injection — if the solution looks cloudy, crystallised, or discoloured (it should be clear and colourless), do not use it and contact your prescriber or pharmacy. Proper storage protects both the medication's effectiveness and your safety throughout your weight management journey.
- 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 Mounjaro freezes?
If a Mounjaro KwikPen freezes (e.g., left in a freezer or extremely cold environment), do not use it. Freezing damages the medication. Discard the pen safely and obtain a replacement from your pharmacy. Always store unopened pens in the main fridge compartment, not the freezer section.
Can I store Mounjaro in a travel case instead of a fridge?
For short trips (a day or two), insulated pen cases with temperature-control packs can maintain the 2–8°C range. For longer journeys, ask your pharmacy about travel-friendly storage options. Once opened, you have 30 days at room temperature, which provides more flexibility for travel.
How do I know if my Mounjaro has been stored incorrectly?
Check the pen before each injection. The solution should be clear and colourless. If it appears cloudy, discoloured, crystallised, or has particles, do not use it. Contact your GP or pharmacy immediately. Incorrect storage is rare if you follow the 2–8°C unopened and below 30°C in-use guidelines.
Do I need to bring my Mounjaro pen to my GP appointment?
Generally, no — but ask your prescriber. If you're having a clinical review, your GP may want to check your storage method or discuss any side effects. Always keep pens in a cool bag or insulated case if transporting them outside your home.
What's the difference between Mounjaro and Wegovy storage requirements?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) follow identical storage guidelines: 2–8°C unopened, below 30°C for 30 days after opening. Check the patient information leaflet that comes with your specific medication, as storage instructions are the same across UK-licensed weight management injections.
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.