Individuals who are psychosis-prone may be more likely to have a psychotic outcome (both acute and long-term) following exposure to cannabis. Psychosis-proneness may be defined on the basis of a psychometric measure or by family history of psychotic disorder. Cannabis exposure has been shown to be associated with higher rates of psychotic outcomes in individuals with higher scores on measures of psychosis-proneness [19, 92, 211, 228]. Similarly, individuals with a high risk for developing psychosis (either because of family history or prodromal symptoms) have higher rates of psychotic outcomes associated with cannabis use [15, 41, 119, 150, 154]. McGuire [150] reported that that individuals who developed acute psychosis after cannabis exposure were more likely to have a positive family history of schizophrenia than patients who screened negative for cannabis use. Recently Arendt [15] showed that risk of psychiatric disorders in first-degree relatives of individuals treated for cannabis-induced psychosis were the same as in those of individuals treated for schizophrenia, suggesting that cannabis causes psychotic symptoms mainly in those who are predisposed to psychosis.
