Hallucinogens are ancient drugs. They have been used for thousands of years in religious ceremonies, as sources of inspiration for artists, as medicines, and of course for some simply as a means of altering their perceptions of the physical world. In America, although the consumption of certain hallucinogens has been a part of religious practice among native peoples for many generations, to the general public, the decade of the 1960s is most closely linked with these drugs, popularly called psychedelics. During this decade, widespread experimentation with LSD, peyote, and "magic mushrooms" influenced many aspects of American pop culture. San Francisco emerged as the mecca for psychedelic "love-ins," beatnik poetry readings, and music called acid rock and psychedelic rock. The image of long-haired hippies wearing beads and tie-dyed clothes and speaking in psychedelicinfluenced language is etched in popular memory. Many people...