Characterizing the Effects of Extended Cannabis Abstinence on Cognitive Function in Patients with Schizophrenia and Non-psychiatric Controls with Cannabis Dependence

Background: While chronic cannabis use impairs cognition in controls, paradoxically, cannabis-using patients with schizophrenia demonstrate better cognitive function than non-using patients. It has been proposed that this relationship is driven by a higher functioning patient subgroup (trait effect) that is cognitively less impaired than their non-using counterparts. A caveat, however, is that most studies employed cross-sectional designs making it difficult to draw firm conclusions regarding causality. AIM: Therefore, we used a 28-day cannabis abstinence period to investigate the state-dependent effects of cannabis on key cognitive outcomes (e.g., HVLT, SDR, Digit Span) in cannabis dependent schizophrenia patients versus non-psychiatric controls. Hypothesis: We predicted that abstaining participants would experience improvements in working memory, and verbal memory and learning performance over time, and expected patients to have greater magnitude of change compared to controls. Method: Nineteen patients and 20 non-psychiatric male cannabis dependent participants underwent 28 days of cannabis abstinence. Cognition was assessed biweekly on Day 0, 14 and 28 using a comprehensive battery. Clinical symptoms were assessed weekly. Abstinence was encouraged using weekly therapy sessions and low cost contingency management confirmed by twice weekly urine assays. Results: Fort-two percent of patients and 55% of controls achieved end-point abstinence. This was biochemically verified by full cannabis elimination (Day28 urinary THC-COOHPh.D