Causal association between cannabis and psychosis: examination of the evidence
Louise Arseneault, Mary Cannon, John Witton
and Robin M. Murray
BRITISH JOURNAL OF PSYCHIATRY(2004)
There is little dispute that cannabis intoxication can lead to acute transient psychotic episodes in some individuals (D’Souza et al, 2004) and that it can produce short-term exacerbation or recurrences of pre-existing psychotic symptoms (Thornicroft, 1990; Mathers & Ghodse, 1992; Hall & Degenhardt, 2004). However, controversy remains about whether cannabis use can actually cause schizophrenia or other functional psychotic illness in the long term (Johns, 2001).
A previous review paper,published more than a decade ago, reached no firm conclusion regarding causality and stressed the importance of prospective longitudinal population-based cohort studies to elucidate a possible causal association (Thornicroft, 1990). Sixteen years after the publication of the first evidence that cannabis may be a causal risk factor for later schizophrenia (Andre´asson et al,1988), four recent prospective epidemiological studies have provided further evidence.We review the evidence from these studies within the framework of established criteria for determining causality.