History, rationale and potential of human experimental hallucinogenic drug research in psychiatry.

Systematic scientific interest in psychedelic substances has a tradition of about 100 years. Numerous human experimental studies have confirmed the existence of a common nucleus of experiences in hallucinogen-induced states and the acute stages of schizophrenic psychoses. However, the degree of resemblance between endogenous and drug-induced psychotic states has been an issue of controversial debate. After the scheduling of psychedelics in the 1960s, human research became highly restricted worldwide and scientific interest in this field faded. The debate about the appropriateness of the psychedelic state as a model for endogenous psychosis therefore seemed to have little practical relevance. Currently there is a revival of scientific interest in human experimental psychedelic research. Consequently, the appropriateness of hallucinogen-induced states as models for psychosis needs to be reappraised. The arguments for and against are summarized in this paper. In conclusion, the drug-induced model psychosis is shown to be a useful model for acute psychotic stages, but not for the nosological entity schizophrenia.