The study included 124 subjects with diagnoses of
schizophrenia or
schizoaffective disorders according to the DSM III-R. Inclusion criteria for participation in the study were age 18 years or older and willingness to provide consent to participate in the study. The inpatients were evaluated when their condition was stabilised. Assessment tools were the psychoactive
substance use disorder section of the Composite International Diagnostic Interview (CIDI), the Positive and Negative Syndrome Scale (PANSS), the Global Assessment of Functioning Scale (GAF). Subjects with
cannabis abuse or dependence during their lifetime were compared with subjects without abuse or dependence, using chi(2) test for categorical variables and analyses of covariance (ANCOVA) for quantitative variables.
RESULTS: Forty-nine subjects (42,6%) presented lifetime abuse or dependence on one or more substances. Since 19 patients with alcohol, stimulant,
sedative or
opiate abuse or dependence were excluded, the study finally included 96 subjects including a first group of schizophrenic patients with
cannabis abuse (n=6) or dependence (n=24) and a second group without any psychoactive
substance abuse (n=66). Thirteen (11.3%) patients presented
cannabis abuse or dependence within the 6 months prior to the assessment. The mean SD age of onset of
cannabis abuse or dependence was 19.6 +/- 3.0 years.
Cannabis abuse/dependence preceded the first psychiatric treatment in 70% of the subjects (n=21). 83.3% of the schizophrenic patients with
cannabis abuse or dependence were male (n=25) compared to 62.1% in the group without
substance abuse (n=41) (chi(2)=4.32, df=1, p=0.04). Schizophrenic patients with
cannabis abuse were significantly younger (mean age: 28.9 +/- 6.3 vs 37.0 +/- 12.7, ANCOVA, F=7.2, df=1,96 p=0.009). There was no significant difference between the two groups for marital status, (chi(2)=5.34, df=2, p=0.07), level of education, (chi(2)=0.93, df=2, p=0.62) professional status, (chi(2)=8.7, df=5, p=0.11), on PANSS total score (ANCOVA, F=0.42, df=1,93, p=0.52), GAF score (ANCOVA, F=0.06, df=1,92, p=0.80), mean number of hospitalizations (ANCOVA, F=3.25, df=1,85, p=0.08), mean age of first psychiatric contact (ANCOVA, F=0.74, df=1,93, p=0.39), and
neuroleptic dosages (ANCOVA, F=0.03, df=1,90, p=0.87). In contrast, the total duration of hospitalization was significantly longer for the group with
cannabis abuse. Patients with
cannabis abuse were more likely to have an history of suicide attempts than subjects without
substance abuse (chi(2)=11.52, df=1, p=0.0007).
DISCUSSION: The prevalence rates for
substance abuse and the socio-demographic characteristics of the population of our study are consistent with findings of previous studies. Male gender and age were significantly related to history of
cannabis abuse or dependence.
Cannabis abuse frequently preceded the onset of psychiatric treatment. However, both
schizophrenia and
substance abuse tend to develop gradually, with no clear demarcation for the onset of
schizophrenia. The absence of any link between the scores for the subscales of the PANSS and
cannabis abuse, both in our study and in some retrospective previous studies, is not suggestive of
cannabis abuse as a
self-medication of positive or negative symptoms of
schizophrenia.
Self-medication could concern other symptoms, such as cognitive deficits. In addition, the hypothesis of
self-medication has especially been suggested in
cocaine abuse or dependence. Some limitations to this study can be discussed. First, although the recruitment was systematic and done in a public mental health service, the patients of our study are not necessarily representative of all schizophrenic patients. Secondly, as in any retrospective study, the prevalence of lifetime
substance abuse may have been under-estimated. Urinary toxicology tests may have been able to improve the sensitivity of the diagnosis of recent
substance abuse, but structured interviews are more appropriate for the diagnosis of lifetime
substance abuse in schizophrenic patients than urinary toxicology tests.
CONCLUSION: