The theory proposes that drug abuse is an outcome of a drug-related identity change process that is set in motion by three micro-level concepts, two meso-level concepts, and three macro-level concepts. The micro-level concepts are personal marginalization, ego identity discomfort, and lost control in defining an identity. The meso-level concepts are social marginalization and identification with a drug subcultural group. The three macro-level concepts are economic opportunity, educational opportunity, and popular culture. Together, they describe a motivation for drug-related identity change and an opportunity structure for that change. The theoretical model contains 12 hypothetical relationships that describe the links between the micro, meso, and macro-level concepts. This theory focuses specifically on drug abuse, whereas the leading theories of drug abuse causes tend to focus more on drug users than on drug abusers or not to distinguish between the two. Thus far, the cultural-identity theory holds that drug abusers are likely to be individuals who experience a significant amount of personal and social marginalization and whose ego-identify discomfort escalates because of it. The theory describes a process that individuals can get off and on at different times in their lives. Both quantitative and qualitative methods would be useful for examining the theory empirically. Figure, notes, and 128 references (Author abstract modified)