If your Mounjaro KwikPen isn't working as expected, don't panic. Most issues come down to technique, priming, or a needle problem — all easy to fix. A small number of cases are genuine faults that need a replacement. This article walks you through both.
Before troubleshooting
- Wash your hands and work in good light
- Take the pen out of the fridge 15-30 minutes before use — cold pens feel stiffer
- Never force the pen. Forcing can damage the mechanism or affect dose delivery
- Never try to take the pen apart
My Mounjaro pen feels stiff or hard to push
This is usually normal, especially with your first few injections. The KwikPen is designed with deliberate resistance to make sure each dose is accurate. Most patients find the pen feels easier after a few uses as they get used to the steady pressure required.
If it feels excessively stiff:
- Make sure the pen has warmed to room temperature
- Try a fresh needle — a damaged or bent needle increases resistance
- Use steady, moderate pressure — pressing too fast makes the plunger feel jammed
- Hold the pen at a 90° angle to your skin
My Mounjaro pen isn't clicking
The click confirms full dose delivery. If you don't hear one:
- Check the grey cap is fully off
- Make sure the dose counter shows the correct dose
- Press the button fully and hold for 5-10 seconds
- Hold the pen firmly against your skin throughout
If the pen still doesn't click, stop and contact us. Don't force it.
My Mounjaro pen looks like there's medication left after my 4 doses
This is normal. Mounjaro KwikPens contain a small amount of extra medication so you can prime the pen — the goal is not to use every last drop. A clear liquid visible in the pen after your 4th dose is expected.
What is not normal:
- Large amounts of medication remaining with doses still unused
- Dose counter showing remaining doses but no medication delivered
- Being unable to complete all 4 prescribed doses from one pen
If any of those apply, contact us.
My Mounjaro pen is leaking
- Before injection: the pen may be defective. Do not use it. Contact us
- During or after injection: you may not have received the full dose. Do not inject again. Contact us for guidance
Keep the leaking pen — we may need it returned for investigation.
My Mounjaro pen is jammed mid-injection
- Stop pressing the button
- Remove the pen carefully from your skin
- Do not try to repair or reuse the pen
- Contact us for a replacement
How to check if your pen is genuinely faulty
- The medication inside should look like water — clear, with no particles or cloudiness
- The dose counter should turn smoothly and show clear numbers
- The pen body should be undamaged — no cracks or leaks
- Tilt the pen at eye level: the liquid should move freely
If any of these checks fail, the pen is faulty.
What we do if your pen is faulty
- Contact our team with your order number and a description of the issue (photos help)
- Our pharmacist will assess and confirm if the pen is faulty
- We will arrange a replacement at no cost
- Faulty pens are returned to Eli Lilly (the manufacturer) for investigation — we handle the return process for you
- We may also submit a Yellow Card report to the MHRA
Keep the original packaging and all pen components until we've spoken — the manufacturer needs these for their investigation.
If you have any concerns about your treatment, contact our support team. For medical emergencies, call 999 or 111.