An Open Multicentric Randomized Clinical Trial Assessing the Impact of Motivational Interviewing on Cannabis Consumption in Patients With Psychiatric Disease

Schizophrenia is a severe mental illness with a lifetime morbidity risk close to 1 %, involving both genetic and environmental risk factors. Prospective studies have shown that heavy use of cannabis in adolescence moderately increases the risk of developing schizophrenia. Many data have also suggested that the co-occurrence of cannabis abuse in patients with schizophrenia has a deleterious impact on the clinical outcome of schizophrenia. Cannabis abuse by schizophrenic patients is a significant public health problem for which there is no empirically validated treatment. We are presently studying the efficiency of motivational therapy on cannabis consumption in patients with schizophrenia.

330 patients with schizophrenia and cannabis abuse or dependence (according to DSM-IV criteria) are randomly assigned to 4 motivational interview during one month or usual intensive treatment. Treatment is conducted in outpatient which are evaluated at the inclusion and at 6 month with Time-Line Follow Bach for the consumption, PANSS score, number of relapse...). A outcome measure was urinalysis results providing an objective measure of cannabis use throughout the six month of the trial.