Lysergic Acid Diethylamide, commonly known as LSD or acid, is a powerful hallucinogenic drug. It was first synthesized in 1938 by Swiss chemist Albert Hofmann and has been used recreationally since the 1960s. LSD produces profound changes in consciousness, including altered states of perception, mood, and thought. It can also cause intense visual and auditory hallucinations. LSD is illegal in most countries and is classified as a Schedule I drug in the United States.