You used the drug Ultrajet once too often and now your body is craving for more... and more... and more... well done! You got yourself addicted.
Ultrajet addiction is a form of addiction which can occur in Fallout 3, Fallout: New Vegas and was cut from Fallout 4.
Fallout 3, Fallout: New VegasEdit
Ultrajet has a 20% chance of Addiction, resulting in a -2 penalty to Agility and Strength as well as -1 to Perception.
Ultrajet addiction is permanent, meaning it cannot be cured by doctors or Fixer.
An addiction to Ultrajet was intended to have a penalty of -1 to Agility and -15 to Action Points. It was never implemented into the game and only exists in the game files. Instead, Ultrajet causes a regular jet addiction in Fallout 4.