Criminal responsibility and cannabis use: psychiatric review and proposed guidelines

An evaluation of the criminal responsibility of an offender who has consumed cannabis necessitates knowledge of the effect of the product on the offender's mental state at the time of the alleged offense. However, the effects induced by cannabis are numerous and the forensic psychiatrist should base his diagnosis and his evaluation on facts which are as objective as possible. A selective literature review, using the computerized databases Medline, Psychlit and Embase, has been carried out to aid evaluation from a forensic psychiatry point of view. Biological means of cannabis detection, and the difficulties associated with using them to understand the clinical effect that the product has on any one user, are shown. Eight major categories which can be used in the domain of forensic psychiatry are detailed in this review: Acute usual effects, acute adverse effects, mood disturbance, acute toxic confusion, acute psychotic reaction, chronic paranoid psychosis, amotivational syndrome or other long term effects, and flashbacks. For each of these categories the effects of cannabis intoxication on cognitive and volitional capacities are analyzed, and guidelines for the evaluation of criminal responsibility are proposed.