Aims: This study examined the longitudinal association between reductions in cannabis use and changes in anxiety, depression, sleep quality, and quality of life. Methods: Secondary analyses were conducted based on data from a cannabis use disorder medication trial in 302 adults (ages 18-50). Changes in symptoms of anxiety and depression, sleep quality, and quality of life were assessed in relation to changes in cannabis use during the 12-week trial of treatment Results: Based on the slope of individual cannabis use trajectory, the sample was classified into two groups (Cannabis Use Reduction, n = 152 vs. Cannabis Use Increase, n = 150) which was included as a binary covariate in subsequent modeling. Controlling for demographics (age, gender,race/ethnicity), treatment condition, and time varying tobacco and alcohol use, separate latent growth curve models showed a significant association between the Cannabis Use Reduction group and improvement (i.e., lower values in slope) in anxiety (13 = -.09, SE = 0.04; p <0.05), depression (13 = -0.11, SE = 0.04; p < 0.01), and sleep quality (13 = -0.07, SE = 0.03; p < 0.05) over the observation period, but not in quality of life. Conclusions: These results indicate a longitudinal relationship between reductions in cannabis use and improvements in anxiety, depression, and sleep quality. Clinicians treating patients with co-occurring cannabis use and problems with anxiety, depression, or sleep quality should attend to cannabis use reduction as a component of treatment. (C) 2017 Elsevier Inc. All rights reserved.