The Comorbidity and Trauma Study (CATS) has been previously described 35 (link), 36 (link). Briefly, opioid dependent patients were recruited from OST clinics in the greater Sydney area of Australia between 2003 and 2008, a period during which the vast majority of the sample were likely to be either currently receiving, or to have previously received, methadone treatment. Ethics approvals were obtained from the institutional review boards of University of New South Wales, Washington University in Saint Louis, Queensland Institute of Medical Research and the relevant NSW area heath service. The current analyses were restricted to individuals who met DSM-IV criteria for opioid dependence. During the interview, opioid dependent individuals were asked if they ever had a period of abstinence from opioids. Those endorsing such a period were asked if they ever had a subsequent relapse. Genotyping was performed using the Illumina Human660W-Quad BeadChip at the Johns Hopkins Center for Inherited Disease Research (CIDR) and principal components were identified using the smartpca program in the Eigensoft 3.0 package 37 (link). An additive model was used in logistic regression analysis to examine the effect of rs10485058 genotype on relapse in 1215 patients of European descent, while controlling for age, sex, and two principal components.