To summarize the discussion of the two competing concepts, “gateway” sequence and common addiction liability, the following points can be reiterated. Juxtaposed with the parsimonious and empirically proven concept of CLA, explaining comorbidity of substance use disorders and polydrug abuse by commonality in etiologic mechanisms, the GH appears redundant. Considering the numerous exclusions from and the triviality of the “typical” substance use initiation sequence, as well as its irrelevance to substance use disorders, its utility is uncertain. Taking into account the danger that the presentation of that sequence as a “theory” may be (and has been) erroneously interpreted in causal terms, it may be hindering both research and intervention. In contrast, CLA, a behavioral/psychological trait, manifests in a range of “gateway” behaviors grounded in the mechanisms of socialization and affective/cognitive regulation with deep evolutionary roots. The CLA concept provides theoretical and empirical foundation to research in etiology, quantitative risk and severity measurement, and targeted non-drug-specific intervention. This conclusion is supported by the papers in this special issue.
