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 Does An Empty Mounjaro Pen Look Like?
When your Mounjaro KwikPen is empty, several visual indicators will help you recognise it has no medication left. Understanding what an empty pen looks like is important so you can safely dispose of it and ensure you don't accidentally attempt to inject without medication. This UK health guide explains the key signs to watch for, how to check your dose counter, and what steps to take once your pen is finished. If you're using tirzepatide as part of your weight management plan, knowing when to replace your pen is essential.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
Visual Signs Of An Empty Mounjaro Pen
An empty Mounjaro KwikPen displays several clear visual cues. The most obvious sign is the dose counter on the side of the pen will show "0" — this is your primary indicator that all four weekly doses have been used. When you look at the pen from the side, you may notice the plunger at the bottom is fully depressed, indicating the medication reservoir is empty. The pen's window (where you can sometimes see the solution inside) may appear cloudy or show no visible liquid, though this is less reliable than checking the dose counter.
- Dose counter displays zero
- Plunger fully pushed down at the base
- No visible solution in the viewing window
- Pen feels lighter than a full pen
- The click mechanism may feel different when attempting to dial a dose
Each Mounjaro KwikPen contains four pre-filled doses (four weeks' worth of medication). The dose counter automatically decreases by one after each weekly injection, so you always know exactly how many doses remain. Never attempt to inject if the counter reads zero — this confirms the pen is empty.
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.
What To Do When Your Mounjaro Pen Is Empty
Once your Mounjaro pen reaches zero on the dose counter, dispose of it safely and prepare a new pen for your next scheduled injection. Store your empty pen in a sharps bin or return it to a pharmacy for safe disposal — never put it in general household waste. If you've been prescribed Mounjaro through an NHS specialist service, contact your weight management clinic to request your next supply. For private prescriptions, your online prescriber or pharmacy will guide you on ordering your replacement pen.
Storage of new pens: Keep unopened pens in the refrigerator at 2–8°C until needed. Once you start using a new pen, it can be kept at room temperature (below 30°C) for up to 30 days. Check the expiry date on the carton before using. Your GLP-1 weight loss calculator can help you track projected progress as you continue your treatment with each new pen.
- 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.
How many doses are in one Mounjaro pen?
Each Mounjaro KwikPen contains four pre-filled doses, providing medication for four weeks of once-weekly injections. After each injection, the dose counter decreases by one. When it reaches zero, the pen is empty and should be disposed of safely.
Can you refill an empty Mounjaro pen?
No. Mounjaro KwikPens are pre-filled, single-use devices and cannot be refilled. Once empty, dispose of it safely in a sharps bin or at your pharmacy. You'll need to obtain a new pen for your next dose.
What if the dose counter doesn't match the plunger position?
The dose counter is the most reliable indicator of remaining doses. If you notice a discrepancy, contact the pharmacy where you obtained the pen — this may indicate a defective device that should be reported.
How should I dispose of an empty Mounjaro pen?
Place your empty Mounjaro pen in a sharps bin (available from pharmacies or your GP surgery) or return it to your pharmacy for safe disposal. Never put it in general household waste or recycling, as the needle poses an injury risk.
Can I tell if a pen is empty just by weight?
An empty pen does feel noticeably lighter than a full one, but this isn't a reliable method on its own. Always check the dose counter, which clearly shows zero when no doses remain. The counter is the definitive way to confirm your pen is finished.
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.