In sum, studies of adolescent alcohol and marijuana use indicate weaknesses in neuropsychological functioning in the areas of attention, speeded information processing, spatial skills, learning and memory, and complex behaviors such as planning and problem solving even after 28 days of sustained abstinence (Brown et al. 2000; Medina et al. 2007a; Tapert and Brown 1999, 2000; Tapert et al. 2002). There are also associated changes in brain structure and function that include altered prefrontal, cerebellar, and hippocampal volumes, reduced white matter microstructural integrity, and atypical brain activation patterns (Bava et al. 2009; Hanson et al. 2010; Jacobsen et al. 2007; Medina et al. 2010; Schweinsburg et al. 2005b, 2008; Tapert et al. 2001b, 2004, 2007). There may be potential reversibility of brain structural changes with long-term abstinence (Delisi et al. 2006), though additional studies are needed to understand the extent to which abnormalities persist or remit with time. Further, the potential interaction of alcohol and marijuana are of concern considering that comorbid use is common (Medina et al. 2007a).
