White matter maturation during adolescence through young adulthood is important for neuronal transmission between connecting brain regions. A recent study comparing adolescent marijuana users and matched controls indicated no significant differences in white matter volumes 37. However, marijuana use (β = .42, p < .04) and smaller white matter volume (β = −.34, p < .03) each predicted increased depressive symptoms on the Hamilton Depression Rating Scale 38. Further, marijuana use interacted with white matter volume to predict depression scores on the Beck Depression Inventory (BDI) 39. White matter volume was negatively associated with depressive symptoms on the BDI, such that less white matter volume was associated with more depressive symptoms in adolescent marijuana users only (β = −.59, p < .03). Although between-group differences were not found in overall white matter volume, it seems plausible that marijuana use may cause or be linked to subtle alterations in white matter tracts that are responsible for mood regulation and depressive symptoms.
