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 You Keep Mounjaro In The Fridge?
Yes, unopened Mounjaro KwikPens must be stored in a refrigerator at 2°C to 8°C until you start using them. However, once you've used a pen for the first time, you can keep it at room temperature below 30°C for up to 30 days. Understanding the correct storage conditions is essential to ensure your tirzepatide injection remains effective and safe to use. This guide covers everything UK patients need to know about storing Mounjaro safely 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 Rules — Before And After First Use
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. Unopened pens can be used until the expiry date printed on the carton if kept refrigerated properly. Never freeze Mounjaro — if a pen has been frozen, do not use it.
After first use: Once you inject your first dose, the pen can be stored at room temperature below 30°C for up to 30 days. After 30 days from first use, dispose of the pen safely, even if medication remains. This applies whether the pen has been used once or multiple times during that 30-day window.
- Keep away from heat and direct sunlight at all times
- Do not store in a car dashboard or window
- If travelling, use an insulated cooling pack to maintain temperature
- Mark the first-use date on your pen so you know when the 30-day window expires
Clinically BackedWeight Loss
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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.
Mounjaro Vs Wegovy — Storage And Practical Differences
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) follow similar storage rules: refrigerate unopened, room temperature after first use for up to 30 days. However, there are key differences worth knowing. Mounjaro is a dual GIP and GLP-1 receptor agonist, whereas Wegovy is a GLP-1 agonist only. Both are prescription-only weight management injections available in the UK following clinical assessment. Mounjaro KwikPens contain four weekly doses, while Wegovy pens also contain a month's supply. Your prescriber will discuss which medication suits your individual health needs — storage requirements alone should not influence this decision.
- 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 refrigerate Mounjaro after opening it?
Yes, you can refrigerate an opened Mounjaro pen if you prefer, but it's not required. Opened pens can be stored at room temperature below 30°C for up to 30 days. Some patients choose to refrigerate for convenience or to extend the usable window, though the 30-day limit still applies from first use.
What if Mounjaro accidentally freezes?
Do not use a frozen Mounjaro pen. Freezing damages the medication and makes it unsafe to inject. Always thaw frozen medication — never attempt to use it. Contact your prescriber or pharmacy for a replacement pen if this happens.
How do I know when to dispose of my Mounjaro pen?
Mark the date you first use your pen on the carton. Dispose of it 30 days later, regardless of how much medication remains. Never use a pen beyond 30 days after first use. Dispose of used pens in a sharps bin or return them to a pharmacy.
Can I travel with Mounjaro on a plane?
Yes, Mounjaro can travel with you. Carry it in hand luggage in an insulated cooling bag with ice packs to maintain 2–8°C. Check airline rules in advance — most allow prescription medications in carry-on bags. Never pack in checked luggage where temperatures may drop below freezing.
Does storage affect how well Mounjaro works?
Proper storage is crucial for effectiveness. Frozen or overheated Mounjaro loses potency and becomes unsafe. Following storage guidelines — refrigerate unopened, room temperature after opening — ensures your injection works as intended and delivers the expected weight loss support.
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.