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
What to Do with Your Empty Mounjaro Pen
When your Mounjaro KwikPen runs out of doses, you'll need to dispose of it safely and arrange a new prescription. In the UK, empty insulin pens and similar devices must be disposed of as clinical waste, not in regular household bins. This guide explains the correct disposal process, storage of used pens, and how to request your next prescription from your GP or prescriber.
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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.
How to Safely Dispose of Your Empty Mounjaro Pen
An empty Mounjaro KwikPen should never be placed in household waste. Instead, you must return it to a pharmacy or GP surgery for safe disposal as clinical waste.
- Return to a pharmacy: Take your empty pen to any pharmacy (a UK pharmacy, Lloyds, a UK pharmacy, or a local independent chemist). They have sharps bins and are trained to handle needles and injection devices safely.
- Return to your GP surgery: Your GP surgery has clinical waste disposal facilities and can dispose of the pen correctly.
- Never dispose in household bins: Empty pens contain needles and residual medication — they pose a safety risk to waste workers and the environment.
- Sharps bin alternative: If you use multiple injections, ask your pharmacy for a sharps bin (a small yellow clinical waste container) for home use. This keeps all used pens together safely.
Your prescriber will typically issue a new prescription before your current pen empties, so you can collect it from your chosen pharmacy.
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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.
Storing Your Mounjaro Pen Before and After Use
Before first use: Store unopened KwikPens in a fridge at 2–8°C in the original carton, away from light. Do not freeze.
After first use: Once you've injected your first dose, the pen can be kept at room temperature (below 30°C) for up to 30 days. After 30 days from first use, discard safely even if doses remain.
An empty pen — one where all 4 doses have been used — should be returned for disposal immediately. Do not store empty pens at home. Using our GLP-1 weight loss calculator can help you plan your Mounjaro journey and understand dose escalation, so you know when to expect each new pen delivery.
- 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 refill my empty Mounjaro KwikPen?
No, Mounjaro KwikPens are single-use devices and cannot be refilled. Each pen contains 4 pre-filled doses. Once empty, you must dispose of it safely and request a new pen from your prescriber. A new prescription will typically be issued before your current pen empties.
What if my Mounjaro pen has been open for more than 30 days?
Discard it safely through a pharmacy or GP surgery. Mounjaro is only assured to be safe and effective for 30 days after first use at room temperature. After 30 days, the medication may have degraded, even if doses remain in the pen.
Do I need a prescription for every Mounjaro pen?
Yes. Each new pen requires a separate prescription from your GP or online prescriber. Your prescriber will review your progress, check for side effects, and confirm you're ready to continue before issuing the next prescription. This is part of safe, monitored weight management care.
Where is the safest place to dispose of a used Mounjaro pen in the UK?
Any community pharmacy (a UK pharmacy, Lloyds, a UK pharmacy, local independent chemist) or your GP surgery. Both have clinical waste disposal facilities specifically for needles and injection devices. Never put it in household rubbish or recycling bins.
How long does one Mounjaro KwikPen last?
Each KwikPen contains 4 doses, which lasts 4 weeks (since you inject once weekly). Your dose may be increased every 4 weeks during the titration phase, so you'll need a new pen each month until you reach your maintenance dose. A new prescription should arrive before your current pen empties.
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.