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
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How Do I Store Mounjaro?
Proper storage of your Mounjaro KwikPen is essential to keep the medication safe and effective. Whether you've just received your prescription or are managing ongoing doses, understanding the correct storage conditions helps protect your tirzepatide and ensures it works as intended. This guide covers refrigeration requirements, room temperature rules, and what happens after you first use your pen.
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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.
Unopened Mounjaro Storage — Refrigeration Rules
Unopened Mounjaro KwikPens must be stored in a refrigerator at between 2°C and 8°C (standard fridge temperature). Keep the pens in their original carton to protect them from light exposure. Do not freeze your Mounjaro — if a pen has been frozen, it should not be used.
- Store at 2–8°C (fridge temperature) — do not freeze
- Keep in the original carton to block light
- Can be used until the expiry date printed on the carton if stored correctly
- Check the temperature of your fridge with a thermometer if you're unsure
- If your fridge fails or power is lost, contact your pharmacy for guidance
When you first receive your Mounjaro prescription, place the KwikPen box immediately in the fridge. Do not leave it at room temperature while unpacking — cold chain integrity from pharmacy to your home is important.
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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.
After First Use — Room Temperature Storage
Once you've used your first dose from a Mounjaro KwikPen, you can store the pen at room temperature (below 30°C) for up to 30 days. This makes it practical to carry with you or store in a drawer at home.
- Room temperature storage permitted for up to 30 days after first use
- Keep away from direct heat and sunlight
- A bathroom cabinet away from hot water pipes is suitable
- Dispose of the pen 30 days after first use, even if medication remains
- Do not refrigerate the pen again after removing it for room temperature storage
Mark the date you first used the pen on the carton so you remember the 30-day deadline. After 30 days, dispose of the used pen safely in a sharps bin — ask your pharmacy for a free sharps bin if you don't have one.
- 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 a regular kitchen fridge?
Yes, a standard kitchen fridge at 2–8°C is perfectly suitable. Keep the KwikPen in its original carton to protect it from light. Check your fridge temperature with a thermometer to ensure it stays in the correct range. Avoid storing it near the freezer compartment where it could accidentally freeze.
What if I accidentally froze my Mounjaro?
Do not use a frozen Mounjaro KwikPen. Contact your pharmacy or prescriber immediately to report the issue. A frozen pen may not work properly or be safe to inject. Your pharmacy can arrange a replacement or advise whether the pen is safe to use based on the specific circumstances.
Can I travel with Mounjaro and keep it at room temperature?
Yes. Once you've used the first dose, you can carry the KwikPen in a bag at room temperature (below 30°C) for up to 30 days. For longer trips, a small insulated cool bag with an ice pack (not ice directly touching the pen) can maintain cool temperatures. Always keep it away from direct sunlight and heat sources like car dashboards.
How do I dispose of a used Mounjaro KwikPen?
Place the used pen in a sharps bin — a yellow plastic container designed for needles and injections. Your pharmacy will provide a free sharps bin when you collect your first prescription. When full, return the sealed bin to your pharmacy or local waste disposal point. Never throw used pens in household waste.
Does Mounjaro storage differ from Wegovy?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) have similar storage requirements — refrigerate unopened at 2–8°C, room temperature after first use for up to 30 days. However, Mounjaro and Wegovy are different medications with different mechanisms and doses. Always follow the specific instructions for whichever medication your prescriber has recommended.
Ready to take control of your weight loss journey?
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