Fallout, Fallout 2, Fallout Tactics
Buffout has a 25% chance to cause addiction. It lasts for a week, beginning 48 hours after consumption. When addicted, one suffers a 2 point penalty to Strength and Endurance and a 3 point penalty to Agility.
Fallout 3, Fallout: New Vegas
Buffout has a 10% chance to cause addiction. The penalties of being addicted have been significantly lowered, as being addicted only causes a 1 point penalty to Strength and Endurance.
Fallout 4, Fallout 76
Buffout, Buffjet, and Bufftats respectively have 25%, 35%, and 35% chance to cause addiction. When addicted, the player character suffers a 1 point penalty to Strength and Endurance. The addiction can be cured by visiting a doctor, taking addictol, eating a radscorpion egg omelette or drinking a refreshing beverage.