You used the drug Jet once too often and now your body is craving for more... and more... and more... well done! You got yourself addicted.
Jet addiction is a form of addiction which can occur in Fallout 2, Fallout 3 and Fallout: New Vegas.
Everything is moving so slowly... you need to get some more Jet, right NOW!
”— Fallout 2 In-game description
Jet has a 50% chance to cause addiction. When addicted to Jet, it gives a -1 penalty to Strength and Perception.
Fallout 3, Fallout: New VegasEdit
Jet has a 20% chance to cause addiction. When addicted to Jet, it gives a -1 penalty to Agility and Charisma.