He served as deputy director of the Office of National Drug Control Policy from 2009 to 2012.

He has since worked for the Veterans Administration Medical Center in Philadelphia and the University of Pennsylvania.

McLellan was the principal developer of the Addiction Severity Index (ASI) and the Treatment Services Review (TSR), widely used substance abuse instruments.

McLellan served as the deputy director of the Office of National Drug Control Policy under the Obama administration.

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