The malleability of the liability phenotype, including “maturing-out” of conditions satisfying diagnostic criteria for dependence (e.g., Dawson et al., 2006), holds promise for effective intervention. To potentially guide research, the time points for the ontogenetic trajectory can be specified as age periods, at which distinct factors influencing addiction liability and its development may be identified. For instance, the genotype, which is the program of this development with all its individually possible variants, is determined at the moment of conception. The range of these variants, comprising the individual norm of reaction, is narrowed during development as the liability phenotype forms under individual environmental conditions. Some of those environmental influences are profound (e.g., intrauterine exposure to teratogens impairing brain development), may have various lengths of period-specificity related to the different organizational levels of impact and different developmental periods (e.g., lead neurotoxicity, attachment problems, maltreatment, imitation of “adult” behavior), and are likely mediated by epigenetic changes. A major growth in risk, corresponding to a shift of the population liability distribution to the right, occurs during the peripubertal period and is strongly associated with
