How the Mounjaro Pen Works
The Mounjaro pen is a pre-filled device that delivers your medication automatically, so you don’t need to measure anything yourself. Each pen contains four doses and is used once a week.
The injection is given under the skin (subcutaneously). You can inject into your stomach or thigh, or someone else can help inject into the back of your upper arm.
Each pen comes with:
5 needles (including one spare)
A sharps' bin for safe disposal
What the Pen Should Look Like After Each Dose
After each injection, the dose window should return to “0”. You may also notice the grey plunger gradually moving down after each use - this is expected and shows the pen is being used correctly.
Once all four doses have been used, the pen will no longer turn to “1”. Even if you can still see a small amount of liquid inside, this is normal. The pen is designed so that a small amount remains and cannot be used.
At this stage, the pen is finished and should be disposed of safely.
How to Use Your Pen
Please watch these video for a step-by-step guide on how to use your injection pen:
- How to use Mounjaro pen
Why can't I twist my dose knob?
If you are unable to turn the dose knob to select your medication, it is usually due to one of two reasons:
All four doses have been used: Mounjaro pens are designed to deliver exactly four doses. Once the fourth dose is administered, the knob will automatically lock. Even if you see a small amount of liquid remaining, the pen is finished and should be safely disposed of.
If you haven't reached the 4-dose limit, the mechanism may be jammed. Try gently wiggling or tapping the end of the dial while turning it, as this can loosen the plunger mechanism and allow you to load the dose.
Why can't I push my dose knob in?
If you feel significant resistance or the pen feels "jammed" when you try to inject, the medication has no clear path to flow through the needle. This is typically caused by:
Needle Caps: You may have forgotten to remove one or both of the protective needle caps (the outer clear cap and the inner green cap).
Improper Attachment: The needle hasn’t properly pierced the red rubber seal (septum) at the top of the pen.
Blockages or Damage: The needle may be bent, damaged, or blocked. This frequently happens if a needle is reused or if the pen was stored without its protective cap, allowing the rubber seal to dry out or collect debris.
Reusing Needles: Using the same needle more than once can lead to the tip dulling or the medication crystallizing inside the needle, causing a total blockage.
How to fix a pen that won't press in
If the dose button feels hard to press, do not force it. Applying force can permanently damage the pen.
Applying excessive pressure will not fix the blockage and could permanently damage the internal mechanism of your pen. Instead, follow these steps:
Stop immediately: If you feel resistance, pull the needle away from your skin.
Remove the needle: Unscrew the current needle and dispose of it safely.
Reset the dial: Turn the dose knob back to the '0' position.
Prepare a new needle: Inspect a fresh, sterile needle for any visible damage or bends.
Attach carefully: Screw the new needle onto the pen, ensuring it is straight, so it correctly pierces the rubber seal.
Remove both caps: Ensure both the outer and inner protective needle caps are removed.
Prime the pen: Follow the standard priming procedure (turning to the line and pressing the button) to see a drop of liquid. This confirms the flow is clear.
Administer your dose: You can now redial your dose and proceed with the injection.
Why a Pen Can Become Damaged
The Mounjaro pen is a precision instrument. Never force the dose button if you encounter resistance. If the needle is blocked or improperly attached, the built-in pressure can cause the internal mechanism to fail. Always ensure the needle is securely fitted before injecting.
The red rubber seal at the top of the pen - where the needle screws on - is called the septum. If too much pressure builds up, this septum can become damaged.
Look for these signs:
Bulging: The red seal looks swollen or pushed out.
Bursting: The seal is cracked, torn, or leaking.
Stop: If you see a bulged or burst seal, do not use the pen. It will no longer dispense the medication safely.
The best way to protect your pen is simple:
If the button feels hard to push, stop immediately. Never try to force it. Instead, change the needle and try again.
Still having trouble?
If you have followed these troubleshooting steps and suspect your pen is damaged beyond repair, please reach out to Customer Care. Our team will be happy to review your specific situation and discuss the available options with you.