What we know, and don't know, about cannabis, psychosis and violence

• Published in: New Zealand medical journal Vol. 132; no. 1499; pp. 76 - 77
• Main Authors: Boden, Joseph M, Spittlehouse, Janet K
• Format: Journal Article
• Language: English
• Published: New Zealand Pasifika Medical Association Group (PMAG) 26.07.2019
• Subjects: Alcohol; Cannabis; College professors; Domestic violence; Health Knowledge, Attitudes, Practice; Humans; Marijuana; Marijuana Abuse; Marijuana Use - legislation & jurisprudence; Marijuana Use - psychology; Mental disorders; New Zealand; Psychosis; Psychotic Disorders; Schizophrenia; Violence; New Zealand; United Kingdom > UK
• ISSN: 1175-8716

[...]the press release cited a number of studies and sets of statistics as evidence for their position. Most of the research linking increased risk of violence to psychosis have examined patients with a diagnosis of a psychotic disorder, rather than those with reported symptoms.5 The magnitude of the elevated risk among those diagnosed with a psychotic disorder is relatively small,5 but greater than among those who report symptoms but do not meet criteria for disorder,4 and it is relatively rare for psychosis to precede violent behaviour.6 In addition, many of these studies examined violence among psychiatric inpatients who have been involuntarily committed to hospital due to risk of harm to self or others, suggesting that sample selection may play a strong role in the observation of violent behaviour among these individuals.5 Furthermore, earlier studies that have examined the links between psychotic symptomatology and violence have found that there were a specific subset of symptoms, related to perceived threat and internal control-override that were related to violent behaviour, rather than psychotic symptomatology more generally.7 Therefore, while the risk of violence is elevated among individuals diagnosed with psychosis, the nature of the links between specific features of psychosis and violence is not well understood. [...]the press release also quotes statistics from various jurisdictions in which the influence of cannabis is inferred by the authors of the release, but clearly cannot be shown to be causal.