There is a clear need for effective interventions to reduce cannabis use in patients with first-episode psychosis. This follow-up of a randomized trial examined whether an intervention for parents, based on motivational interviewing and interaction skills (Family Motivational Intervention, FMI), was more effective than routine family support (RFS) in reducing cannabis use in patients with recent-onset schizophrenia.

In a single-blind trial with 75 patients in treatment for recent-onset schizophrenia, 97 parents were randomly assigned to either FMI or RFS. Assessments were conducted at baseline and at 3 and 15 months after the interventions had been ended. Analyses were performed on an intention-to-treat basis using mixed-effect regression models.

From baseline to the 15-month follow-up, there was a significantly greater reduction in FMI compared to RFS in patients’ quantity (p = 0.01) and frequency (p < 0.01) of cannabis use. Patients’ craving for cannabis use was also significantly lower in FMI at 15 months follow-up (p < 0.01). Both groups improved in parental distress and sense of burden; however, only FMI parents’ appraisal of patients’ symptoms showed further improvement at the 15-month follow-up (p < 0.05).

The results support the sustained effectiveness of FMI in reducing cannabis use in patients with recent-onset schizophrenia at 15 months follow-up. Findings were not consistent with regard to the long-term superiority of FMI over RFS in reducing parents’ distress and sense of burden.

Cannabis use by people with schizophrenia has been found to be associated with family distress and poor clinical outcomes. Interventions to reduce drug use in this patient group have had limited efficacy. This study evaluated the effectiveness of a novel intervention for parents of young adults with recent-onset schizophrenia consisting of family-based motivational interviewing and interaction skills (Family Motivational Intervention, FMI) in comparison with routine family support (RFS).

In a trial with 75 patients who used cannabis and received treatment for recent-onset schizophrenia, 97 parents were randomly assigned to either FMI (n=53) or RFS (n=44). Assessments were conducted at baseline and 3 months after completion of the family intervention by an investigator who remained blind throughout the study about the assignment of the parents.

At follow-up, patients' frequency and quantity of cannabis use was significantly more reduced in FMI than in RFS (p<0.05 and p<0.04 respectively). Patients' craving for cannabis was also significantly reduced in FMI whereas there was a small increase in RFS (p=0.01). There was no difference between FMI and RFS with regard to patients' other substance use and general level of functioning. Both groups showed significant improvements in parental distress and sense of burden.

Training parents in motivational interviewing and interaction skills is feasible and effective in reducing cannabis use among young adults with recent-onset schizophrenia. However, FMI was not more effective than RFS in increasing patients' general level of functioning and in reducing parents' stress and sense of burden.