Grant: Doctoral Award - Frederick Banting and Charles Best Canada Graduate Scholarships

Background: Cannabis is the most commonly used drug in schizophrenia, posing as a barrier to overall quality of life. Cannabis use disorders (CUD) in these patients is associated with earlier onset and worsened symptomatology and cognitive/functional impairments that have been shown to improve with cannabis abstinence. Moreover trending legalization of cannabis in 2018 poses a significant threat to this population for which there is no satisfactory treatment. Brain stimulation techniques like repetitive transcranial magnetic stimulation (rTMS) directed to the dorsolateral prefrontal cortex are well-tolerated and may have potential to address co-morbid CUD in schizophrenia, while improving psychiatric symptoms and cognition. Objective: To assess effects of rTMS as a treatment for CUD in schizophrenia patients. Methods: A total of 40 individuals meeting criteria for schizophrenia and CUD between ages of 18-55 will be recruited from the Centre for Addiction and Mental Health (CAMH) in Toronto. Participants will be randomized into either active (n=20) or sham (n=20) high frequency rTMS (20 Hz) groups in a 6-week, double-blind, randomized, parallel controlled trial. All patients will receive contingency management and drug counselling interventions to facilitate 28-day cannabis abstinence trial endpoint, also monitored by THC levels from urine samples. Outcomes: The primary outcome will be trial endpoint self-reported cannabis use assessed by timeline follow-back and confirmed by cannabis urine toxicology. Secondary outcome measures will include cognitive outcomes (verbal learning, working memory and mismatch negativity), cannabis craving and withdrawal, and psychosis symptom ratings (Positive and Negative Symptoms Scale for Schizophrenia, Calgary Depression Scale for Schizophrenia). Significance: The proposed research may improve the health of patients suffering from schizophrenia and comorbid CUD with use of rTMS as a treatment, thereby improving functional outcomes.