Cannabis use is associated with lower retention in methadone maintenance treatment, but not among schizophrenic- and other chronically psychotic patients

Background: The findings of studies on cannabis use and retention in methadone maintenance treatment (MMT) are inconsistent. Objectives: To study cannabis use and its relationship to patients' outcomes in MMT with/without lifetime DSM-IV-TR schizophrenia/chronic-psychosis diagnosis. Methods: Since June 1993, 877 patients with available lifetime DSM-IV-TR psychiatric diagnosis were followed-up until December 2017. Urine drug screens on admission and after one year were analyzed. Results: Lifetime schizophrenia/psychosis was diagnosed in 50 (5.7%) patients. They did not differ from the other 827 by admission cannabis use (18.0% vs. 12.3%) and had similar 1-year retention rates (76.0% vs.77.0%, respectively). Cumulative retention of the cohort excluding schizophrenia/chronic-psychosis was longer for the 667 patients who did not use cannabis after 1-year (9.1 years, 95%CI 8.4-9.9) compared with the 118 cannabis-users after 1-year (6.0 years, 95% CI 4.8-7.2, p<.001). Among the schizophrenia/chronic-psychosis group, cannabis was not related to retention (38 non-users, 7.9 years 95%CI 5.2-10.5 vs. 9 cannabis-users, 9.9 years, 95% CI 3.8-16.0, p=.5). Survival was shorter for the 41 schizophrenia/chronic-psychosis non-users (15.2 years, 95% CI 12.8-17.7) than for the 719 non-schizophrenia/chronic-psychosis non-users (18.5, 95%CI 17.9-19.2, p = 0.009). However, survival was comparable among the 9 cannabis-users with schizophrenia/chronic-psychosis (20.1, 95% CI 16.2-24.1) and 101 other cohort users (18.6, 95% CI 16.9-20.4). Conclusions: Cannabis use is associated with decreased retention among MMT patients, however the effects of cannabis on schizophrenia/psychosis patients on retention and survival cannot be verified due to the small sample size and the limited data regarding chronicity of cannabis use. Future larger, prospective studies are needed.