A replication sample of EAs, informative for opioids but not cocaine, was derived from the Comorbidity and Trauma Study (CATS) [30, 31]. Briefly, opioid-dependent cases age 18 or older were recruited from opioid agonist treatment (OAT) clinics in metropolitan Sydney, Australia. Persons who had recent suicidal intent or psychosis were excluded. Controls were recruited from neighborhoods geographically proximal to the cases and excluded those who used opioids recreationally more than five times. Subjects were interviewed using the Semi-Structured Assessment for the Genetics of Alcoholism-Australia (SSAGA-OZ) [32] to derive DSM-IV substance use disorders (SUDs) diagnoses.
