Cannabis use itself was associated with a modest increase (3.18%) in left (but not right) hippocampal volume. This finding contradicts prior studies that have linked chronic, but not occasional, cannabis use to decreases (not increases) in hippocampal volume. We speculate that the association between cannabis use and increased hippocampal volume may be due to the nature of DNS, which includes casual, non-problem users who are also likely enriched for other factors that might protect against progression to problem use (and against hippocampal deficits). In support of this, we found that cannabis users in DNS were more likely to represent higher socioeconomic status (t=3.70, p<0.001) and even showed modest increases in digit-span performance (t=2.50, p =.013), an index of working memory suggesting that cannabis users in DNS may be characterized by adaptive factors that protect them from progression to problem use. Therefore, if previously documented associations between cannabis use and smaller hippocampal volumes are a consequence of chronic exposure to cannabis, then we would not expect to see these reductions in the DNS.
