Several models have been proposed to explain the interaction between cannabis exposure and psychosis-proneness. It may be that the psychosis-prone individuals are attracted to using cannabis (an association model), or that cannabis use increases psychosis-proneness (a causal model), or that there is another factor that causes both psychosis-proneness and cannabis use (an indicator-variable model) [91, 193]. While cannabis users tend to exhibit higher psychosis-proneness scores in some [54, 200, 235] but not all studies [55, 193], psychosis-prone individuals are not more likely to use cannabis [92]. Recently, Veling et al. [227] showed that individuals with schizophrenia had higher rates of cannabis use than either their siblings or controls, while their siblings had similar rates of cannabis use to controls, suggesting (1) that cannabis use predicted schizophrenia and (2) that risk for developing schizophrenia did not confer a higher risk for cannabis use.
