Psycho Addiction

Psycho addiction is a form of addiction which can occur in Fallout, Fallout 2, Fallout 3, Fallout: New Vegas, Fallout 4, Fallout 76 and Fallout Tactics.

Fallout, Fallout 2, Fallout Tactics
Psycho has a 20% chance to cause an addiction. It lasts for a week. When addicted, the player character suffers a 2 point penalty to Intelligence.

In Fallout Tactics, the penalty is very different: Damage Resistance is reduced by 25 and Agility by 3, while Intelligence is actually increased by 1.

Fallout 3, Fallout: New Vegas
Psycho has a 10% chance to cause an addiction. When addicted, the player character suffers a 1 point penalty to Endurance and Perception.

Fallout 4, Fallout 76
Psycho, Psychobuff and Psychojet have a 25%, 35% and 35% chance respectively to cause an addiction. When addicted, the player character suffers a 1 point penalty to Strength and 10 to Damage Resistance. The addiction can be cured by visiting a doctor, taking addictol, eating a radscorpion egg omelette or drinking a refreshing beverage.

Behind the scenes
The picture is a reference to several horror movies. The hockey mask refers to Friday the 13th, the long claws refer to A Nightmare on Elm Street and the chainsaw is a nod to The Texas Chainsaw Massacre as it says "Made in Texas."