To test hypotheses about patterns of familial association between attention-deficit/hyperactivity disorder (ADHD) and psychoactive substance use disorders (PSUDs) by using the family study method.
The first-degree relatives of clinically referred children and adolescents with ADHD (131 probands, 413 relatives) and healthy control probands (106 probands, 323 relatives) were assessed by blind raters.
After stratifying the probands with ADHD and the control probands into those with PSUD (group 1 and group 3, respectively) and those without PSUD (group 2 and group 4, respectively), familial risk analyses revealed the following: (1) the risk for ADHD was not significantly different between relatives of group 2 and group 1 probands (19.6% vs 18.0%; P=.88), but these 2 risks were significantly greater than the risk to relatives of group 3 probands (1.0%; P=.01 and P=.02, respectively) and group 4 probands (7.0%; P=.001 and P=.01, respectively); (2) there were no significant differences in the risk for PSUD between relatives of group 1 (47.5%) and group 3 probands (39.7%; P=.40), but these risks were greater than the risk to relatives of group 2 (30.0%; P=.32) and group 4 probands (20.9%; P<.001); and (3) there was no evidence for nonrandom mating.
These findings are consistent with the hypothesis that ADHD and PSUD are transmitted independently in families. Because the probands were young adolescents, many have not lived through the age at risk for PSUD. Thus, the hypothesis stating that ADHD and PSUD represent variable expressions of a common underlying risk factor cannot be ruled out.