The cannabinoid receptor gene (CNR1) is thought to modulate the striatal response to rewarding stimuli [32] and polymorphisms of this gene are associated with alcoholism and intravenous drug use in humans [39, 179, 194, 241]. A variety of CNR1 polymorphisms have been studied for associations with schizophrenia, with mixed results [33, 125, 144, 197, 221, 222, 240]. However, in a case-only design Zammit et al. [240] failed to find an effect of a CNR1 polymorphism on schizophrenia between those who did not use cannabis and those who claimed to have used cannabis at least 1 year prior to illness onset.
