Methodological issues of human experimental research with hallucinogens.

Human experimental research with hallucinogenic drugs is potentially able to identify linking variables between the psycho(patho)logical conditions and neurobiological alterations involved in both pharmacologically induced and naturally occurring acute psychotic states. A number of methodological aspects should be considered when planning modern experimental studies with hallucinogenic drugs. The issues of subject selection, repeated measures, and adequate control groups are discussed in this paper. Examples of recent experimental studies are presented which take these aspects into account. The first study examined psychopathological changes, facial expression and semantic priming effects during a psilocybin-induced state. In the second study, semantic priming effects after intake of psilocybin, 3,4-methylenedioxyethylamphetamine (MDE), and d-methamphetamine were investigated. Results confirmed time-dependent effects of psilocybin and the restriction of increased priming effects in the psilocybin group.