Variable individual sensitivity to cannabis in patients with schizophrenia.

There is now compelling evidence that cannabis consumption might precipitate psychosis onset. The objective of the present study was to assess the role of individual sensitivity to the psychotogenic effect of cannabis in male patients with schizophrenia. The lifetime diagnosis, disease and substance-use history were determined using a standardized interview in 190 patients with schizophrenia. Of patients with lifetime cannabis use (n=121), 44 were characterized as Cannabis-sensitive (CS) patients if the onset of psychotic symptoms occurred within 1 month following the initiation of cannabis consumption, or following a marked rise of cannabis consumption, or marked aggravation of psychotic symptoms each time the subject used cannabis. Age at onset of psychosis was not different in patients with lifetime cannabis use compared to non-users. By contrast, the first psychotic episode occurred 2.6 yr earlier in CS compared to Non-cannabis-sensitive (NCS) patients (p=0.006). Moreover, a specific excess of family history of psychotic disorder was found in CS patients, but not of any other psychiatric disorder, as well as an earlier age at exposure to cannabis (16.7+/-2.5 yr, p=0.03). Sensitivity to psychotogenic effects of cannabis in schizophrenia patients could be related to both genetic vulnerability to schizophrenia and the influence of cannabis on brain maturation and could modulate the influence of cannabis on the onset of schizophrenia.