A prospective study of cannabis use as a risk factor for non-adherence and treatment dropout in first-episode schizophrenia.

INTRODUCTION: Although several studies have reported on cannabis use and adherence for first episode of psychosis patients, the findings remain unclear as to whether cannabis use is a risk factor for poor adherence in young people with first-episode schizophrenia. This study was designed to follow patients' use of cannabis and adherence in a naturalistic setting during the first 12 months of treatment. It examines whether cannabis use is a risk factor for two distinct types of non-adherence: non-adherence to medication and treatment dropout.
METHODS: Participants were 112 first-episode schizophrenia patients of diverse backgrounds at two community hospitals, enrolled in a study of differential effectiveness of two second-generation antipsychotic medications. Multiple indicators were used to assess cannabis use and adherence to medication. Patients were encouraged to continue in the study even after periods of treatment refusal or change from study to standardized medication. Study hypotheses were tested using Cox proportional hazards models with cannabis use as a time-varying covariate.
RESULTS: After 12 months, 23 had dropped out and 37 had at some point been non-adherent to medication. Of 34 participants who used cannabis during treatment, 32 had a prior diagnosis of cannabis abuse/dependence and 30 were male. Independently of age, race, socioeconomic status, gender, site, and medication assignment, cannabis use significantly increased hazard of non-adherence by a factor of 2.4 (p<.001) and hazard of dropout by a factor of 6.4 (p=.034).
CONCLUSION: Results indicate that cannabis use is a risk factor for non-adherence to medication and dropout from treatment. Treatment for first-episode schizophrenia may be more effective if providers address the issue of cannabis use with patients throughout the early years of treatment, especially for those with existing cannabis abuse/dependence.