A total of 9340 subjects (GWAS: n = 5799, replication: n = 3541) were recruited for genetic studies of alcohol, cocaine, and opioid dependence at five US sites using similar methodologies: Yale University School of Medicine (GWAS: n = 2360, replication: n = 1737), the University of Connecticut Health Center (GWAS: n = 2303, replication: n = 1360), the University of Pennsylvania School of Medicine (GWAS: n = 476, replication: n = 228), the Medical University of South Carolina (GWAS: n = 459, replication: n = 192), and McLean Hospital, an affiliate of Harvard Medical School (GWAS: n = 201, replication: n = 24). The institutional review board at each of the participating sites approved the study. Written informed consent was obtained from all participants. Certificates of confidentiality for the studies were issued by the National Institute on Alcohol Abuse and Alcoholism (NIAAA) and the National Institute on Drug Abuse (NIDA).
