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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Do You Have To Keep Mounjaro Refrigerated?
Yes, unopened Mounjaro KwikPen devices must be kept refrigerated at 2 to 8°C to maintain effectiveness. Once you begin using a pen, you can store it at room temperature below 30°C for up to 30 days. Proper storage is essential for ensuring your tirzepatide medication works as intended. Understanding these storage requirements helps you get the most from your prescription and avoid wasting doses.
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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 vs Wegovy Storage Requirements
Mounjaro storage requirements differ slightly from Wegovy due to how each medication is formulated. Unopened Mounjaro pens must be stored in a refrigerator at 2–8°C and kept in the original carton to protect from light. Never freeze Mounjaro — if a pen has been frozen, do not use it. Once you start injecting from a pen, you can keep it at room temperature (below 30°C) for up to 30 days before disposing of it.
Wegovy storage follows similar rules: unopened pens require refrigeration at 2–8°C, and after first use can be stored at room temperature below 25°C for 30 days. Both medications come as pre-filled auto-injection pens designed for convenience, but temperature control matters for stability. This reflects their similar mechanism as GLP-1 and dual GIP+GLP-1 receptor agonists respectively.
- Unopened: Refrigerate at 2–8°C in original carton
- After first use: Room temperature (below 30°C for Mounjaro, below 25°C for Wegovy)
- Duration: 30 days after opening
- Never freeze either medication
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.
Which Medication Suits You — Mounjaro or Wegovy?
Both Mounjaro and Wegovy are prescription-only weight management medications available in the UK, but they work slightly differently. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, whilst Wegovy (semaglutide) is a GLP-1-only medication. Clinical trial data — SURMOUNT for Mounjaro and STEP for Wegovy — shows both can support weight loss when combined with a reduced-calorie diet and increased physical activity. Your prescriber will assess which medication is suitable for your individual health, eligibility, and needs. Storage convenience is similar for both, so this should not be the deciding factor. Use our free GLP-1 weight loss calculator to explore projected outcomes with either medication, and discuss storage practicalities with your prescriber if you have concerns about refrigeration access.
- 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 kept in a regular fridge?
Yes. A standard household fridge that maintains 2–8°C is ideal for storing unopened Mounjaro pens. Keep the pens in their original carton to protect them from light. Do not store them in the freezer compartment — freezing damages the medication.
What happens if Mounjaro freezes?
If a Mounjaro pen has been frozen, it should not be used. Freezing can alter the medication's chemical structure and reduce its effectiveness. Always store unopened pens in the main fridge compartment, not the freezer.
How long can Mounjaro stay out of the fridge after opening?
After you inject your first dose, the Mounjaro pen can be kept at room temperature (below 30°C) for up to 30 days. After 30 days, dispose of the pen safely even if doses remain — the medication may no longer be stable.
Is Mounjaro storage different from Wegovy?
Storage is very similar. Both require refrigeration unopened (2–8°C), both can be kept at room temperature after opening (Mounjaro below 30°C, Wegovy below 25°C), and both should be used within 30 days of first injection. Storage requirements should not influence which medication your prescriber recommends.
What if I don't have reliable fridge access?
Discuss this with your prescriber or pharmacist. Some people use portable cooler bags or pen cases with cooling packs when travelling. Your prescriber needs to know about storage challenges so they can advise whether Mounjaro is practical for your situation — alternative options may be available.
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.