A brief historical overview of psychedelic research.

Classical serotonergic psychedelics such as lysergic acid diethylamide (LSD) or the naturally occurring compounds psilocybin and mescaline produce profound changes in mood, thought, intuition, sensory perception, the experience of time and space, and even the experience of self. Research examining psychedelic compounds has had a complex and turbulent evolution. Many cultures throughout the world used psychedelic plants for mystical, ritualistic, or divinatory purposes, but also to cure illnesses. Much of the genesis and progress of modern investigations into the effects and underlying mechanisms of action of psychedelics have been intertwined with studies of the neurotransmitter serotonin. Early hypotheses that serotonergic systems mediate psychedelic effects were supported initially by preclinical animal studies and subsequently confirmed by pharmacological studies in healthy humans. The use of psychedelic compounds as putative psychotomimetics reproducing some features of naturally occurring psychotic disorders met with some limited success. More recent studies are exploring psychedelics as potential psychotherapeutics. Recent indications that even one or two psychedelic treatments produce robust and sustained reductions in clinical symptoms in a variety of psychiatric disorders have prompted an enormous resurgence of interest into the nature and mechanisms contributing to their effects.