The current findings should be considered in the context of limitations and strengths of this study. The associations studied here are correlational and cannot be used to infer a causal influence of OPRM1. Although the sample size is equivalent to other alcohol administration studies of OPRM1 (Ray et al., 2012b; Ray and Hutchison, 2004, 2007; Setiawan et al., 2011), the relatively small sample is a limitation, particularly in the context of retrospective genotyping. The lack of a placebo control condition or an alternative reinforcer may also be considered a limitation. The current design cannot rule out the possibility that more frequent alcohol requests among GA/GG participants reflected motivational processes unrelated to desired level of intoxication; for example, one study found associations of OPRM1 with approach bias for alcohol stimuli as well as other appetitive stimuli (Wiers et al., 2009). Strengths of this study include the high degree of experimental control afforded by CASE and the focus on a young sample.
