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
Do You Have to Store Mounjaro in the Fridge?
Yes, unopened Mounjaro KwikPens must be stored in a refrigerator at 2°C to 8°C to maintain effectiveness. However, 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 tirzepatide in the UK, whether through NHS specialist services or private prescription routes. Incorrect storage can damage the medication and reduce its effectiveness for weight management.
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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 Requirements — Before and After First Use
Unopened Mounjaro pens must always be stored in a refrigerator between 2°C and 8°C. Keep them in the original carton to protect from light, and never freeze them — if a pen has been frozen, do not use it. Mounjaro can remain in the fridge until the expiry date printed on the carton, making it safe to stock supplies in advance of your weekly injections.
After first use, you can store the pen at room temperature (below 30°C) for up to 30 days. This flexibility means you don't need to carry a cold bag to work or when travelling short distances. However, you must dispose of the pen 30 days after first injection, even if medication remains. Keep used pens away from heat and direct sunlight to prevent degradation. These storage rules apply whether you're using tirzepatide through NHS specialist weight management services or a private prescription.
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.
Accessing Mounjaro in the UK — NHS and Private Routes
NHS access is through tier 3 specialist weight management services. Your GP can refer you, though waiting lists vary significantly by region and can be lengthy in many areas. NICE has approved tirzepatide for NHS use, making it available without private cost once referred.
Private access is faster — prescription-only Mounjaro is available through UK-licensed online prescribers following a clinical assessment. Private costs typically range from £150–£300 per month depending on your dose. A standard Mounjaro KwikPen (four weeks' supply) costs between £120–£250 privately. Both routes require proper storage guidance, which your prescriber or pharmacist will provide when dispensing.
- 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 Mounjaro be left out of the fridge overnight?
No. Unopened Mounjaro must always be refrigerated at 2–8°C. Once you've started using a pen, you can leave it at room temperature for up to 30 days, but unopened pens should never be left unrefrigerated for extended periods.
What happens if Mounjaro freezes?
Do not use a frozen Mounjaro pen. Freezing damages the medication and makes it unsafe and ineffective. Always store unopened pens in the fridge, never in the freezer compartment.
How long can I keep a used Mounjaro pen at room temperature?
You can store a used pen at room temperature (below 30°C) for up to 30 days after the first injection. After 30 days, dispose of it in a sharps bin, even if medication remains inside.
Does Mounjaro cost more if I need refrigeration at home?
No. Storage requirements don't affect the cost of Mounjaro. Private prescriptions cost £150–£300 monthly regardless of storage. NHS access is free once referred to specialist services, with no additional storage costs.
Can I travel with Mounjaro without a cool bag?
If travelling for less than 30 days with an already-opened pen, you don't need a cool bag — room temperature storage is fine. For unopened pens or longer trips, use an insulated travel case or cool bag to maintain 2–8°C. Your prescriber can advise on travel packs.
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.