Are Patients with Schizophrenia Reliably Reporting their Cannabis Use? An African Cross-sectional Study

Abstract

Background: Most studies of the prevalence of cannabis use among patients with schizophrenia used a self report as declared by the patient himself. We hypothesize that patients with schizophrenia did not tell the truth and might underreport their use for many reasons to be discussed later. Indeed, the under-report of cannabis use among these patients can affect the effectiveness of their treatment. Aims: to assess the degree of agreement between the prevalence values obtained from patients’ reports and the results of the toxicological tests. Methods: A cross-sectional study was carried out on 403 patients with schizophrenia. For each patient, a profile containing sociodemographic, psychiatric history and his illicit drug use was performed. We assessed the patients with Positive and Negative Syndrome Scale (PANSS), Calgary Depression score (CDSS), Baratt Impulsiveness Score (BIS-10) and Medication Adherence Rating Scale (MARS). The consumption of cannabis used was confirmed with MINI International Neuropsychiatric Interview (MINI-DSM IV) and using toxicological analysis. Results: Among the 403 patients who consented to give their urine samples, 49.1% of them (198/403) tested positive for cannabis and 41.41% (82/198) underreported their use. The sensitivity and specificity of the questionnaire were 0.58 and 0.74. Based on the comparison between sociodemographic and psychiatric history data of patients who self-report and underreport their cannabis use, no significant difference was observed except the duration of cannabis use and the score of the medication adherence scale. Moreover, it was found that the impulsivity, PANSS score, CDSS score, and the type of schizophrenia are not involved in the prediction of the underreporting of cannabis use. Conclusion: The rate of patients who under report cannabis use is important. Therefore, toxicological analysis is becoming relevant for the identification of drug use among schizophrenic patients and in the addictive comorbidity research field.