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. You can inject into your stomach or thigh, or someone else can inject into the back of your upper arm.
Each pen comes with:
5 needles, including one spare.
A sharps bin for safe disposal.
All Mounjaro pens contain four doses of 0.6 mL solution. The total amount in the pen is 2.4 mL, regardless of your dose strength.
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 moving down after each use. This is expected and shows the pen is being used correctly.
After all four doses have been used, the pen will no longer turn to 1. A small amount of liquid may remain, but it cannot be used. The pen is finished and should be safely discarded.
How to Use Your Pen
Watch the instructional video in the original Help Centre article for a step-by-step guide.
Why can't I twist my dose knob?
This usually happens for one of two reasons:
All four doses have been used: The knob locks automatically after the fourth dose. Even if a small amount of liquid remains, the pen is finished.
The mechanism is jammed: If you have not used all four doses, gently wiggle or tap the end of the dial while turning it. This may loosen the plunger mechanism.
Why can't I push my dose knob in?
Significant resistance usually means the medication does not have a clear path through the needle. Possible causes include:
Needle caps: One or both protective caps may still be attached.
Improper attachment: The needle may not have pierced the red rubber seal correctly.
Blockage or damage: The needle may be bent, damaged, or blocked.
Reusing needles: A reused needle can become blunt or blocked by crystallised medication.
How to fix a pen that won't press in
Do not force the button. Applying excessive pressure can permanently damage the pen.
Stop immediately: If you feel resistance, pull the needle away from your skin.
Remove the needle: Unscrew it and dispose of it safely.
Reset the dial: Turn the dose knob back to 0.
Prepare a new needle: Inspect a fresh sterile needle for damage or bends.
Attach it carefully: Screw it onto the pen straight so it correctly pierces the rubber seal.
Remove both caps: Take off the outer and inner protective needle caps.
Prime the pen: Turn to the priming line and press the button. A drop of liquid confirms the flow is clear.
Administer your dose: Redial the dose and proceed with the injection.
Why a Pen Can Become Damaged
The Mounjaro pen is a precision instrument. If a blocked or improperly attached needle creates too much pressure, the internal mechanism or red rubber seal, called the septum, can become damaged.
Look for:
Bulging: The red seal looks swollen or pushed out.
Bursting: The seal is cracked, torn, or leaking.
⚠️ If the seal is bulging, burst, or leaking, do not use the pen. It may no longer dispense medication safely. If the button feels hard to push, stop and change the needle rather than applying more force.
Still having trouble?
If you have followed these troubleshooting steps and suspect the pen is damaged beyond repair, contact Customer Care. The team can review the situation and discuss the available options.