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, unopened Mounjaro (tirzepatide) KwikPen devices must be stored in a refrigerator at 2°C to 8°C to maintain their effectiveness. Once you begin using a pen, it can be kept at room temperature (below 30°C) for up to 30 days. Understanding proper storage is essential for anyone prescribed Mounjaro through the UK NHS or private prescription services, as incorrect storage may compromise the medication's potency and your weight management results.
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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 vs Wegovy Storage Requirements
Mounjaro storage rules are straightforward. All unopened pens must stay refrigerated at 2°C to 8°C in their original carton, away from light. Never freeze Mounjaro — if accidentally frozen, discard the pen. Once you inject your first dose, the used pen can be kept below 30°C (room temperature) for up to 30 days before disposal.
Wegovy storage follows nearly identical guidelines. Like Mounjaro, Wegovy (semaglutide) pens must be refrigerated unopened at 2°C to 8°C and can be kept at room temperature after first use for up to 30 days. Both injections are delivered as pre-filled pens — Mounjaro is a KwikPen — so storage conditions are similar. The key difference lies in their mechanisms: Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1 agonist only. Despite this mechanistic difference, both require identical cool storage for unopened supplies.
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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 for UK Users
Keep your Mounjaro in the main fridge compartment, not the freezer or door (where temperature fluctuates). Many UK patients find a dedicated shelf in the back works best. Once you start injecting, mark your pen with the start date so you remember the 30-day room temperature window. If you travel, consider a small cool bag or ask your GP about travel storage solutions. Your prescriber or the patient information leaflet included with your KwikPen can clarify any storage questions specific to your batch. Our free GLP-1 weight loss calculator can help you track expected outcomes while you maintain proper medication storage.
- 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 in the fridge door?
No. Fridge doors experience temperature fluctuations that can affect the medication. Store unopened Mounjaro in the main fridge compartment at 2°C to 8°C, away from the door, in its original carton.
What happens if Mounjaro freezes?
If accidentally frozen, the pen must be discarded — do not use it. Freezing damages the medication. Always keep Mounjaro in the fridge section, never the freezer compartment.
How long can I keep Mounjaro out of the fridge after starting it?
Up to 30 days at room temperature (below 30°C). Mark the start date on your pen to track this window. After 30 days, dispose of it safely.
Is Wegovy storage different from Mounjaro storage?
No. Wegovy follows identical storage rules: refrigerate unopened at 2°C to 8°C, then keep at room temperature for up to 30 days once started. Both are once-weekly injectable pens with the same cold storage requirements.
What should I do if my Mounjaro has been left out of the fridge?
If it has been out for less than 30 days at room temperature, it should still be safe to use. If left out longer or in excessive heat (above 30°C), contact your prescriber or pharmacist for guidance before using it.
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.