Hallucinogens, also known as psychedelic drugs, alter perception and can cause hallucinations. Some examples include LSD, DMT, PCP, and marijuana. Albert Hofmann first synthesized LSD in 1938, and hallucinogenic mushrooms have been used for thousands of years for religious or medicinal purposes by ancient cultures. While some advocate for medical uses, hallucinogens are currently illegal and can have harmful physical, emotional, and social effects if abused.