Verbal learning in marijuana users seeking treatment: a comparison between depressed and non-depressed samples

Abstract

Background: Both individuals with marijuana use and depressive disorders exhibit verbal learning and memory decrements. Objectives: This study investigated the interaction between marijuana dependence and depression on learning and memory performance. Methods: The California Verbal Learning Test – Second Edition (CVLT-II) was administered to depressed (n = 71) and non-depressed (n = 131) near-daily marijuana users. The severity of depressive symptoms was measured by the self-rated Beck Depression Inventory (BDI-II) and the clinician-rated Hamilton Depression Rating Scale (HAM-D). Multivariate analyses of covariance statistics (MANCOVA) were employed to analyze group differences in cognitive performance. Pearson’s correlation coefficients were calculated to examine the relative associations between marijuana use, depression and CVLT-II performance. Findings from each group were compared to published normative data. Results: Although both groups exhibited decreased CVLT-II performance relative to the test’s normative sample (p < 0.05), marijuana-dependent subjects with a depressive disorder did not perform differently than marijuana-dependent subjects without a depressive disorder (p > 0.05). Further, poorer CVLT-II performance was modestly associated with increased self-reported daily amount of marijuana use (corrected p < 0.002), but was not significantly associated with increased scores on measures of depressive symptoms (corrected p > 0.002). Conclusion: These findings suggest an inverse association between marijuana use and verbal learning function, but not between depression and verbal learning function in regular marijuana users.

• Cannabis
• cognition
• comorbidity
• CVLT
• depression
• Marijuana
• neurocognitive
• neuropsychological
• verbal learning

Acknowledgements

The authors gratefully acknowledge the research staff at the Substance Treatment and Research Service (STARS) of Columbia University Medical Center/New York State Psychiatric Institute for their assistance in data collection. Funding for this research was provided by NIDA grants R01 DA15451, P50 DA09236 and K24 DA029647.

Notes

*Portions of this research were presented at the 2010 meeting of the College on Problems of Drug Dependence.

¹Z-scores were employed for this comparison since the CVLT-II manual only provides means and SDs for z-scores for the normative population.

²One MJ + Dep participant who reported an extraordinarily high amount of daily marijuana use (20.9 GM/day) was deemed an outlier, and thus removed from the GM use/day-CVLT-II Total Learning scatterplot for visual clarity; the correlation was significant with and without this outlying data (p < 0.002).