adolescence and adulthood [9]. This has led to the broad consensus that while familial environment is more important for the early stages of experimentation and substance use, genetic factors exert a more pivotal role in later stages of addiction [10, 11]. Twin studies also substantiate the role of common genetic underpinnings to a variety of addictions, including those involving a host of illicit drugs, alcohol, nicotine, and even caffeine (e.g., [12]). This genetic comorbidity extends beyond addictions to other externalizing problem behaviors as well, including general disinhibitory behavior (e.g., [13•]).
