Submitted for Publication: March 6, 2012; final revision received June 7, 2012; accepted July 3, 2012.
Published Online: January 2, 2013. doi:10.1001/jamapsychiatry.2013.282
Author Contributions: Dr Nelson had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Conflict of Interest Disclosures: None reported.
Funding/Support: This work was supported by grants R01 DA017305 (Dr Nelson) and R01 DA23668 (Dr Agrawal) from the National Institute on Drug Abuse and by the National Drug and Alcohol Research Centre and the Australian National Health and Medical Research Council (Dr Degenhardt).
Additional Contributions: Anthony Caracella, BSc, provided sample receipt and preparation, Megan Campbell, BAppSc, provided project coordination, Lisa Bowdler, BAppSc, and Sara Smith, BBiomedSci, provided sample genotyping, and Michelle Torok, MSocSc, Elizabeth Conroy, PhD, Elizabeth Moore, PhD, Caitlin McCue, BHSc, and Cherie Kam, BN, assisted with data collection.