The discovery sample was derived from the Yale-Penn sample, a cohort of 11,439 participants (5758 AAs and 5681 EAs) recruited through treatment centers and advertisements for genetic studies of cocaine, opioid or alcohol dependence11. All participants were interviewed using the Semi-Structured Assessment for Drug Dependence and Alcoholism (SSADDA)12, which we have previously shown to be reliable with respect to both diagnoses and diagnostic criteria13,14, to derive lifetime diagnoses for dependence on these and other substances and other major psychiatric disorders. DSM-IV dependence on stimulants (including amphetamine-related substances) was assessed using information from the SSADDA. Individuals who had a dependence on other stimulants (including cocaine and caffeine) were not considered as stimulant dependent in order to minimize genetic heterogeneity in the outcome and detect variants specifically relevant to dependence on amphetamines and closely related stimulants. Additional details of participant recruitment and assessment are reported elsewhere11,15. After excluding participants with missing stimulant use or basic demographic information, the remaining sample consisted of 614 small nuclear families (1355 total participants) and 10,084 unrelated individuals. An independent sample consisting of 532 EA cases, 7635
