The CAT Study is a case–control examination of genetic and environmental factors contributing to liability for opioid dependence. One thousand four hundred and sixty‐eight cases (577 female [39.3%]) were recruited from opioid substitution therapy (OST) clinics in the greater Sydney region and 513 controls (284 female [55.4%]) from geographic areas in proximity to OST clinics who had minimal or no (0–10 times lifetime) opioid misuse (Conroy et al. 2009; Shand et al. 2011; Nelson et al. 2013). Written informed consent was obtained from all participants as per the institutional review board approvals from the University of New South Wales, WUSM, QIMR, and the ethics committees governing the participating clinics. The mean age at interview was 36.4 years (SD 8.6) for cases and 34.7 years (SD 10.6) for controls.
