Verbal Memory Improved in Schizophrenia Patients Who Stopped Using Cannabis for 28 Days

Prospective 28-day cannabis abstinence study with cognitive testing at days 0, 14, and 28. Abstinence was incentivized through contingency reinforcement and verified by twice-weekly urinalysis (THC-COOH < 20 ng/ml at day 28). A comprehensive neuropsychological battery assessed multiple cognitive domains. Clinical symptoms were monitored weekly.

Cannabis use is extremely common among people with schizophrenia, and there has been debate about whether it helps or harms cognitive function in this population. This study provides prospective evidence that abstinence leads to measurable cognitive improvement, particularly in verbal memory, a domain critical for daily functioning and treatment engagement.

The dual diagnosis of schizophrenia and cannabis dependence is one of the most challenging clinical scenarios in psychiatry. This study suggests that addressing cannabis use could meaningfully improve cognitive outcomes in these patients. The large effect size for verbal memory improvement is clinically significant, as memory deficits are among the most functionally disabling aspects of schizophrenia.

Very small sample size (fewer than 10 abstainers per group after dropout). Only male participants. The contingency reinforcement paradigm may not translate to real-world clinical settings. Less than half of participants achieved the full 28 days of abstinence. The study could not determine whether longer abstinence would produce further improvement.