LSD (Lysergic acid diethylamide), commonly called "acid," is the most powerful known hallucinogen.

There is no physical dependence on LSD after continuous use, for there are no withdrawal symptoms after the drug is discontinued.

A small percentage of patients become psychologically dependent and are called "Acid-heads" or "acid freaks".

Its use can lead to violent behavior or self mutilating behavior. It is this fact that is frequently tested on.