Main Paper Unwanted Effects of Hypnosis: a Review of the Evidence and Its Implications

Growing evidence of unwanted consequences of hypnosis in experimental, clinical and entertainment settings is reviewed. Adverse effects are common, may be physiological or psychological, and are mostly short-lived. Facilitating factors include high hypnotizability and cognitive and personal involvement, although effects secondary to hypnosis such as deactivation and anxiety may cause reactions such as headache. The more serious consequences almost exclusively occur in clinical and entertainment applications and have included chronic psychopathology, seizure, stupor, spontaneous dissociative episodes and the resurrection of memories of previous trauma, typically with age regression. Associated phenomena may include physiological events and may be unconsciously mediated. Two cases of first episode schizophrenia, one following hypnotherapy and one following stage hypnosis, are described, the latter in detail. Evidence of affinities between schizophrenia and hypnosis, beginning with Pavlov but largely ignored since, is revisited in the light of contemporary evidence of the neurophysiological mechanisms of hypnosis and schizophrenia, with implications for screening vulnerable individuals. It is concluded that the responsible scientific attitude is to acknowledge and disclose evidence of unwanted sequelae in order to understand mechanisms, improve safeguards and better educate practitioners. As the context of stage hypnosis does not allow adequate safeguards, and practitioners lack qualifications to address adverse reactions, hypnosis for entertainment should be discontinued.