Med-X Addiction (Fallout: New Vegas)

 is a form of addiction

Gameplay
Med-X has a 10% chance of causing addiction. When addicted, the player character suffers a 1 point penalty to Agility and Intelligence.

In the quest Bye Bye Love, a Medicine check allows the player to tell Joana that her 'contracted pupils and involuntary spasms' are signs of Med-X Addiction.