Additionally, there were indications of differences according to primary drug of abuse. Specifically, the largest treatment effects have been found in studies of marijuana use (moderate effect size, g = .51), whereas smaller effect sizes have been found across studies of alcohol, cocaine, stimulants, opiates, and polydrug use (ranging from g = .08 to g = .13). However, at the time of the meta-analysis, there were far fewer studies evaluating CBT for marijuana use compared to alcohol or other drugs, and many of these studies combined CBT with other psychosocial treatments to enhance effects (Magill & Ray, 2009). Clearly, there is room for improvement in enhancing the effectiveness of CBT for substance use disorders.
