Cannabis use and Cognitive Function: Eight Year Trajectory in a Young Adult Cohort.

PubMed – Addiction. 2011 Jul 12. doi: 10.1111/j.1360-0443.2011.03574.x.

Tait RJ, Mackinnon A, Christensen H.
Source
Centre for Mental Health Research, Australian National University. Canberra, ACT, 0200 Centre for Youth Mental Health (Orygen Research Centre), The University of Melbourne Melbourne, VIC, 3010.
Abstract
Aim:  To evaluated the relationship between change in cannabis use and changed cognitive performance over eight years. Design:  We used survey methodology with a cohort design. Setting & Participants:  An Australian community sample aged 20-24 at baseline. Measures:  We assessed cognitive performance with, the California Verbal Learning Test (CVLT) (immediate and delayed) spot-the-word test (STW), symbol digit modality test (SDMT) and digit backwards (DB). Groups of cannabis users were defined from self-reports across three waves as: “never” (n = 420) “remain light” (n = 71), “former light” (n = 231), “remain heavy” (n = 60), “former heavy” (n = 60) and “always former” (since start of study) (n = 679). Planned contrasts within mixed model repeated measures ANOVA was used for longitudinal analysis with an adjusted alpha of .01. Findings:  Data were obtained from 2404 participants with 1978 (82%) completing wave three. At baseline there were significant differences between cannabis groups on CVLT (immediate and delayed) and SDMT. However, after controlling for education, gender, gender by group and gender by wave, there were no significant between group differences and only CVLT immediate recall reached adjusted statistically significant longitudinal change associated with changed cannabis use (group by wave p= .009). Specifically, former heavy users improved their performance relative to remaining heavy users (estimated marginal means: former heavy 6.1 to 7.5: remain heavy 6.4 to 6.6). Conclusions:  Cessation of cannabis use appears to be associated with an improvement in capacity for recall of information that has just been learned. No other measures of cognitive performance were related to cannabis after controlling for confounds.

© 2011 The Authors, Addiction © 2011 Society for the Study of Addiction.

PMID: 21749524 [PubMed – as supplied by publisher]