You used the chem Mentats once too often and now your body is craving for more... and more... and more... well done! You got yourself addicted.
Mentats addiction is a form of addiction which can occur in Fallout, Fallout 2, Fallout 3, Fallout: New Vegas, Fallout 4 and Fallout Tactics.
Fallout, Fallout 2, Fallout TacticsEdit
Mentats have a 15% chance of causing an addiction. It lasts for 1 week. When addicted, it causes a 2 point penalty to Agility and a 3 point penalty to Intelligence.
Mentats carry a 5% chance of causing an addiction. When addicted, it causes a 1 point penalty to Intelligence and Perception.
Fallout: New VegasEdit
In addition to the Mentats as above in Fallout 3, the Courier can craft Party Time Mentats that in exchange for a Charisma bonus of 5 have an addiction risk of 15%, at otherwise the same effects.
All variants of Mentats carry a 25% chance of causing an addiction. When addicted, it causes a 1 point penalty to Charisma. The addiction can be cured by visiting a doctor, taking addictol, eating a radscorpion egg omelette or drinking a refreshing beverage.