and opiates (Allen et al., 2003; Schoedel et al., 2010) negatively impact memory, processing speed and attention. Over the counter (OTC) cough medication containing dextromethorphan has been linked with cortical thickness in adolescents in one study (Qiu et al., 2016), although this outcome has yet been replicated. It is notable that the majority of these aforementioned studies have numerous methodological weaknesses in that they are primarily cross-sectional, have relatively small sample sizes, lack female participants, have low power to disentangle polydrug effects, or have not been validated in younger adolescents. Another issue with this research to date is that polydrug use, which is common in adolescence (Johnston et al., 2017), and co-use of substances is rarely studied. Co-use use can uniquely impact neurocognition (Lisdahl et al., 2013); indeed, preliminary evidence has shown that co-use of alcohol and nicotine (Pennington et al., 2015; Schuster et al., 2016), alcohol and cannabis (Lisdahl et al., 2013; McQueeny et al., 2009; Medina and Shear, 2007; Bava et al., 2009; Jacobus et al., 2009; Elofson et al., 2013; Hanson et al., 2010; Medina et al., 2007a, Medina et al., 2008, Medina et al., 2007b, Medina et al., 2007c), alcohol and cocaine (Medina et al., 2006;
