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
What Happens If Mounjaro Is Not Refrigerated?
Mounjaro (tirzepatide) must be stored in a refrigerator between 2°C and 8°C before first use to remain safe and effective. If your Mounjaro KwikPen is left unrefrigerated, it may become damaged and unsafe to use. This guide explains proper storage rules for this prescription-only weight management injection in the UK, how it differs from Wegovy, and what to do if storage goes wrong.
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 Rules and Temperature Guidelines
Unopened Mounjaro pens must be stored in a refrigerator at 2°C to 8°C and kept in their original carton to protect from light. They can be used until the expiry date printed on the carton if stored correctly. Never freeze Mounjaro — if a pen freezes, it becomes unsafe and must be discarded without use.
After your first injection, you can keep the pen at room temperature (below 30°C) for up to 30 days. After 30 days from first use, the pen must be disposed of safely, even if it contains unused doses. Heat, direct sunlight, and temperature fluctuations all damage the tirzepatide inside.
If Mounjaro is accidentally left out of the fridge for several hours, it may become unstable. Do not use a pen that has been left unrefrigerated for more than a few hours. Contact your prescriber or pharmacy for guidance — they can advise whether it is safe or if you need a replacement. Always check the pen for cloudiness or discolouration before injecting; if it looks abnormal, do not use it.
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.
Mounjaro vs Wegovy: Storage and Prescription Differences
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are once-weekly prescription-only weight management injections licensed in the UK. Both require refrigeration before use: Mounjaro at 2–8°C and Wegovy at 2–8°C. The key difference is mechanism — Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1 agonist only. Clinical trials (SURMOUNT for Mounjaro, STEP for Wegovy) show both can support weight loss alongside a reduced-calorie diet and increased physical activity. Your prescriber will assess which is suitable for you based on individual health factors. Storage rules are similar for both, so proper refrigeration is equally important regardless of which medication you are prescribed.
- 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 should I do if my Mounjaro pen was left out of the fridge overnight?
Do not use it. Contact your GP or the pharmacy that prescribed it immediately. They can assess whether the pen is safe or if you need a replacement. Never assume a pen left out overnight is still safe — tirzepatide degrades when exposed to temperatures outside the 2–8°C range.
Can I keep Mounjaro in a regular fridge door?
Yes, a standard fridge door is fine as long as the temperature stays between 2–8°C. However, avoid storing it near the back where it may be colder, or in a compartment that gets warmer when the door opens frequently. Keep it in the original carton to protect from light.
How do I dispose of a damaged or expired Mounjaro pen?
Take it to a pharmacy in the UK — they have specialist sharps disposal containers for used or damaged injections. Do not throw it in household waste or down the toilet. Most community pharmacies will accept used insulin pens and similar devices for free.
Is Wegovy storage different from Mounjaro storage?
Both Wegovy and Mounjaro have the same storage requirement: refrigerate at 2–8°C before first use, then room temperature (below 30°C) for up to 30 days after opening. Storage rules are identical, so the same precautions apply.
What does "room temperature" mean for Mounjaro storage?
Room temperature means below 30°C — typically 15–25°C. This is safe for up to 30 days after your first injection. Do not store in direct sunlight, near radiators, or in a car — these locations can exceed safe temperatures and damage the medication.
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.