Psychedelic drugs were used extensively in psychotherapy in the 1950s to lower psychological defences and facilitate emotional insight. Thousands of research participants were administered hallucinogens in the context of basic clinical research or therapeutic clinical research, resulting in hundreds of publications. Results across studies were ultimately inconclusive due to such variations in methods and a lack of modern controls and experimental rigour. The growing controversy and sensationalism resulted in increasing restrictions on access to hallucinogens throughout the 1960s (ultimately resulting in the placement of the most popular hallucinogens into Schedule I of the 1970 Controlled Substances Act in the United States).

Renewed human administration research began in the 1990s. Recent clinical studies have administered hallucinogens to evaluate their safety and efficacy in the treatment of psychiatric disorders: specifically, anxiety related to advanced-stage cancer (Grob, 2005), obsessive-compulsive disorder (Moreno, et al., 2006), heroin dependence (Krupitsky, et al., 2007), personal meaning and spiritual significance (Griffiths, et al., 2008), and a meta-analysis of randomized controlled trials of LSD for alcoholism (Krebs,et al., 2012).

Psychedelic-assisted psychotherapy utilizes the acute psychological effects of psychedelic drugs to enhance the normal mechanisms of psychotherapy. The effects of psychedelic psychotherapy are often very pronounced within several days or weeks after a treatment session, but then these effects quickly decline. This phenomenon was termed a “psychedelic afterglow”.

Fhurther research, blinded, randomized, placebo-controlled, methodology should explore the efficacy of hallucinogens.