Two competing frameworks have been proposed to explain the origins of this commonality and account for the development of drug involvement and co-occurrence of addictions to different drugs. The “gateway hypothesis” (GH) connects initiation of use of various drugs by a sequence stated to represent a developmentally staged process. The alternative model of common (general) liability to addiction (CLA) posits non-specific liability to all drug addictions, regardless of the order of use initiation. The two perspectives have substantially different ramifications for research, clinical practice, and health policy.
