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
Can You Put Mounjaro Back In The Fridge?
Yes, you can refrigerate Mounjaro after first use, but only for a limited time. Once you've used your KwikPen for the first time, you can store it at room temperature (below 30°C) for up to 30 days, but you cannot put it back in the fridge after this initial room temperature use period. Understanding Mounjaro storage rules is essential for keeping your tirzepatide medication safe and effective. Improper storage can affect how well the injection works, so getting it right matters.
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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 Rules — Complete Temperature Guide
Unopened Mounjaro KwikPens must be stored in a refrigerator at 2°C to 8°C until you're ready to use them. Keep them in the original carton to protect from light, and check the expiry date regularly. As long as you haven't used the pen yet, you can store it in the fridge until the expiry date printed on the box.
After First Injection, your opened KwikPen can be stored at room temperature (below 30°C) for up to 30 days only. Once this 30-day period ends, you must discard the pen even if it still contains medication. Do not put it back in the fridge at this stage — returning a used pen to the fridge and then removing it again can affect the medication's stability. Keep it away from direct sunlight and heat sources. After 30 days, dispose of your pen safely in a sharps bin or ask your pharmacy for a sharps disposal service.
Never freeze Mounjaro at any stage — if your pen has been frozen, do not use it. Freezing damages the medication and makes it unsafe to inject.
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 — Cost And Routes
In the UK, Mounjaro is available through two routes: NHS specialist weight management services and private prescription. NHS access is through tier 3 or 4 weight management clinics, usually via GP referral, though availability and waiting times vary significantly by region. Private access is faster — you can get a UK prescription through an online consultation with a licensed prescriber, then collect from a GPhC-registered pharmacy. Private costs typically range from £129 to £320+ per month depending on your dose. Your GP can advise on NHS eligibility, or you can arrange a private consultation directly. Use our GLP-1 weight loss calculator to estimate potential outcomes at different Mounjaro doses, and our BMI calculator to check whether you might meet eligibility criteria for either route.
- 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 happens if Mounjaro freezes?
If your KwikPen has been frozen, do not use it. Freezing damages tirzepatide and makes it unsafe to inject. Discard the pen safely and contact your pharmacy or prescriber for a replacement. Always store in a fridge at 2–8°C, never in a freezer.
Can I reuse a Mounjaro KwikPen?
No. Each Mounjaro KwikPen is single-use. Each pen contains four weekly doses (one month's supply). After your fourth injection, dispose of the empty pen in a sharps bin. Do not attempt to refill or reuse it.
How do I know if my Mounjaro has gone bad?
Check for visible particles, cloudiness, or discolouration in the solution — it should be clear and colourless. If it looks discoloured or has particles, do not use it. Also check the expiry date. If in doubt, ask your pharmacy before injecting.
What's the difference between Mounjaro and Wegovy storage?
Both require refrigeration before first use at 2–8°C. After opening, both can be kept at room temperature below 30°C for up to 30 days. The storage rules are identical — the difference is the medication itself (tirzepatide vs semaglutide) and dose escalation schedules.
Can I travel with Mounjaro on a plane?
Yes, you can travel with Mounjaro. Keep unopened pens in your hand luggage in a cooling pouch or insulated bag with ice packs to maintain 2–8°C. Declare it at security. Once opened, store at room temperature (below 30°C) for up to 30 days. Always carry your prescription or a letter from your prescriber.
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.