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 to Store Mounjaro vs Wegovy: UK Storage Guide
If you're prescribed Mounjaro (tirzepatide) or Wegovy (semaglutide) in the UK, proper storage is essential to keep your medication effective. Both are once-weekly injectable GLP-1 medications (Mounjaro is technically a dual GIP+GLP-1 agonist), but they have slightly different storage requirements. Understanding how to store your KwikPen or pre-filled pen correctly helps ensure you get the full benefit from your prescription. This guide compares storage rules for both medications, covering temperature, timing, and disposal. Use our GLP-1 weight loss calculator to explore how these medications may support your weight management journey.
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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.
Storage Requirements: Mounjaro vs Wegovy
Mounjaro (tirzepatide) storage: Unopened KwikPens must be stored in a refrigerator at 2°C to 8°C and kept in the original carton to protect from light. Never freeze Mounjaro — if frozen, the pen cannot be used. Once you start using a pen, you can store it at room temperature below 30°C for up to 30 days, then discard it safely.
Wegovy (semaglutide) storage: Unopened pens are also refrigerated at 2°C to 8°C in the original carton. After first use, Wegovy pens can similarly be kept at room temperature below 25°C for up to 30 days, then disposed of properly.
- Both medications must be protected from direct sunlight and heat
- Both require disposal 30 days after first injection, even if medication remains
- UK prescribers provide disposal guidance — ask your pharmacy or GP about safe needle disposal in your area
- Never share pens between users
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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.
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When to Choose Each Medication: Clinical and Practical Factors
Both Mounjaro and Wegovy are prescription-only medications requiring clinical assessment by a UK-licensed prescriber. The choice between them depends on individual health factors, medical history, and how you respond to treatment — not storage convenience alone. Mounjaro uses a dual GIP+GLP-1 mechanism and may produce different results than Wegovy's single GLP-1 pathway. Clinical trials showed Mounjaro achieved an average weight loss of approximately 15–21% of body weight, while Wegovy showed around 14.9% in the STEP-1 trial. Individual results vary significantly.
Your prescriber will assess which is more suitable based on your health profile, other medications, and personal circumstances. Both require lifestyle changes — diet and activity — alongside medication for best results. Storage and practical administration are secondary considerations; clinical suitability is primary.
- 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 freeze Mounjaro or Wegovy if I'm not using it immediately?
No. Freezing either medication will damage it and make it unusable. Mounjaro and Wegovy must be stored in a refrigerator at 2–8°C before use. If a pen has been frozen, discard it and do not inject.
How long can I keep an opened Mounjaro or Wegovy pen at room temperature?
After your first injection, both pens can be stored at room temperature (below 30°C for Mounjaro, below 25°C for Wegovy) for up to 30 days. After 30 days, discard the pen even if medication remains.
What's the difference between Mounjaro and Wegovy in terms of mechanism?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, activating two natural hormone pathways. Wegovy (semaglutide) is a GLP-1 agonist only, activating a single pathway. This difference may influence weight loss results and side effects between individuals.
Do I need to store my Mounjaro KwikPen differently if I travel?
Yes. Travel insulin cooler bags designed for 2–8°C storage are available and recommended if you'll be away from a refrigerator for more than a few hours. Keep your pen in the original carton inside a cool bag. Avoid direct heat and sunlight during travel.
How do I safely dispose of used Mounjaro or Wegovy pens in the UK?
Ask your GP, pharmacist, or call your local council for needle disposal advice. Many UK pharmacies and GP surgeries have sharps bins where you can deposit used pens for free. Never put used pens in household recycling or general waste.
Ready to take control of your weight loss journey?
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