Cannabis abuse and serious suicide attempts

Aims. To compare the relationship between cannabis abuse/dependence and risk of medically serious suicide attempts in individuals making serious suicide attempts and randomly selected comparison subjects. Design. Case-control comparison. Setting. Cases, a general hospital; controls, the local community. Participants. Cases were 302 consecutive individuals making medically serious suicide attempts; 1028 randomly selected control subjects. Measurements. DSM-III-R mental disorder diagnoses; measures of socio-demographic characteristics and childhood and family experiences. Findings, Of those making serious suicide attempts, 16.2% met DSM-III-R criteria for cannabis abuse/dependence at the time of the attempt, compared with 1.9% of comparison subjects (OR = 10.3; 95% CI, 5.95-17.8, p < 0.0001). Risks of serious suicide attempt were significantly related to a series of socio-demographic and childhood characteristics, and to mental disorders that were co-morbid with cannabis abuse/dependence. When the association between cannabis abuse/dependence and suicide attempt risk was controlled for socio-demographic factors, childhood factors and concurrent psychiatric morbidity, there was a marginally significant association (OR = 2.0; 95% CI, 0.97-5.3, p < 0.06) between cannabis abuse/dependence and serious suicide attempt risk. Conclusions. These results suggested that much of the association between cannabis abuse/dependence and suicide attempt risk arose because: (a) individuals who develop cannabis abuse/dependency tend to come from disadvantaged socio-demographic and childhood backgrounds which, independently of cannabis abuse, are associated with higher risk of suicide attempt, or (b) because cannabis abuse/dependence is co-morbid with other mental disorders which are independently associated with suicidal behaviour. Nevertheless, the possibility remains that cannabis abuse/dependence may make an independent contribution to risk of serious suicide attempt, both directly and through the possible effects of cannabis abuse on risk of other mental disorders.