“…and colleagues ( 2002) found that both substance use and behavior problems may stem from a heritable propensity to externalizing ("acting out," impulsive) behavior. Finally, beyond the finding that impulsivity is a vulnerability to substance use in general, researchers have suggested that impulsivity may predispose some individuals to perceive specific drug classes such as crack cocaine to be especially rewarding (e.g., Carroll & Rounsaville, 1993;Compton, 2000;Khantzian, 1985;Weiss, Mirin, Griffin, & Michael, 1988). Second, results also may be due to the unique behavioral patterns associated with the use of the two drugs.…”