Troubleshoot Faulty Pens

Mounjaro Pen (UK) Troubleshooting Guide – Common Issues and Fixes

If you're experiencing issues with your Mounjaro pen, or you think it may be faulty or broken, try out these troubleshooting steps:


💡 Tips to Prevent Pen Issues

  • Always follow the manufacturer’s instructions when using the pen. It's designed to prime and deliver one full dose per week. The mechanism limits how much you can twist the dose knob so it’s important not to overuse the pen.
  • Never force the pen. These pens are medical devices and should be stored and handled carefully to avoid damage
  • Don’t carry the pen loose in your bag or anywhere it could collect dust or debris. Particles can jam the mechanism.
  • Never twist the dose knob or try to inject without a needle attached. This can create pressure inside the pen, causing the red seal to bulge or break.
  • Don’t reuse needles. This can lead to blockages, contamination, inaccurate dosing and may increase pressure inside the pen.
  • Always remove the needle after you’ve taken your dose. Leaving the needle attached can cause leakage from the pen.
  • When attaching a needle, push it on straight and firmly. Check the inner needle isn’t bent and avoid attaching it at an angle, as this can damage the pen.
  • The needles we supply are push fit. Some needles twist on – if you’re using your own needles always check which type you're using to make sure it’s properly attached.

Troubleshooting Steps

Issue Troubleshooting Steps
Pen / Dose knob is hard to push
  1. Remove any dust or debris from the pen – a firm blow around the mechanism can help.
  2. Attach a new needle and ensure it’s properly seated on the pen and the inner needle is not bent.
  3. Dial back the dose knob to 0.
  4. At 0, gently press the knob. There will only be a small amount of movement – this may release built-up pressure in the cartridge.
  5. Prime the pen as per instructions, removing any air from the cartridge.
  6. Slowly press the dose knob with gentle pressure - it can be a bit stiff but be careful not to force it.
  7. Ensure you fully depress the dose knob and hold it for 10 seconds–the number on the window of your pen should return to 0 after the full dose has been taken.
Pen / Dose knob is hard to twist
  1. Remove any dust or debris from the pen – a firm blow around the mechanism can help.
  2. Reset the pen by slowly twisting the knob back to 0 - It may require a little force but be gentle to avoid damaging the mechanism.
  3. Attach a new needle and ensure it’s properly seated on the pen and the inner needle is not bent.
  4. Prime the pen as per instructions.
No drip of medication when priming
  1. Attach a new needle and ensure it’s properly seated on the pen and the inner needle is not bent.
  2. Prime the pen according to instructions–you can repeat this process up to two times.
Unable to get last dose

If you’ve taken all 4 doses, the pen is finished and should be thrown away after use or 30 days after first use. It’s normal for some medication to remain in your pen after taking all 4 doses–this is to ensure you have enough to prime the pen for each injection. Below is an image of what your pen will look like after each dose.


If you haven’t taken all 4 doses but the pen isn’t working:

  1. Attach a new needle and ensure it’s properly seated on the pen and the inner needle is not bent.
  2. Prime the pen according to instructions–you can repeat this process up to two times.
  3. Ensure you fully depress the dose knob and hold it for 10 seconds–the number on the window of your pen should return to 0 after the full dose has been taken.

An image showing the Mounjaro pen plunger at each position after a dose has been used.

 
Bulging / Broken red seal

This often happens due to pressure build-up from:

  • Using a bent needle when trying to prime or inject.
  • Using the pen without a needle or when a needle is not attached correctly.

If the seal is slightly bulging:

  1. Attach a new needle - ensure it’s correctly attached and the inner needle is not bent
  2. Dial back the dose knob to 0
  3. At 0, gently press the knob. There will only be a small amount of movement – this may release built-up pressure in the cartridge.

If the red seal is fully out or a needle won’t attach properly, the pen can no longer be used – contact us to discuss the next steps.
Dose is leaking out of pen during injection

This usually means:

  • The needle is not attached properly, or
  • The red seal is bulging or broken

To try to resolve this issue:


  1. Attach a new needle - ensure it’s correctly attached and the inner needle is not bent
  2. Dial back the dose knob to 0
  3. At 0, gently press the knob. There will only be a small amount of movement – this may release built-up pressure in the cartridge.

Ensure any wasted doses are logged correctly:

Make sure to check-in or update your log to reflect the doses used from the pen – even if the dose was wasted. This will ensure the wasted dose is accounted for and we notify you correctly when your refill is due.

Still having issues?

If these steps don’t help, you can:

  • Check the official troubleshooting guide from the manufacturer: Troubleshooting Mounjaro Pen

  • Call the manufacturer’s careline on 01256 315 000



Or reach out to our support team with the following information:

  • The date you took the first dose from this pen
  • Whether there has been any leakage from the pen
  • Whether there has been any damage to the red seal on the end of the pen
  • A clear image of the pen showing the amount of liquid remaining
  • A clear image of the red seal at the end of the pen
  • A short video demonstrating the issue you are experiencing

⚠️ Important: Please do not throw away the pen unless you have been instructed to do so by us.

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