Lysergic acid diethylamide, better known as acid or LSD, is possibly the most well known psychedelic drug. Popularized by the 1960s counterculture, LSD made its way into pop culture with public figures like the Beatles admitting to using it. The chemical was also the subject of a wide range scientific study throughout the 20th century, including the CIA’s illegal and controversial Project MKUltra.

LSD alters awareness and perceptions and may also cause hallucinations. It is not chemically addictive but can cause some negative effects like anxiety and paranoia. Some research shows an increased likelihood of developing psychological disorders like schizophrenia in adults with other risk factors.