Nevertheless, instead of serving as indisputable grounds to reject the GH, the numerous deviations from the “gateway” sequence are dismissed by the proponents of the GH as error or random or non-systematic patterns (Kandel, 1975; Kandel and Yamaguchi, 2002). The inadequacy of the GH in its explaining away the “errors” may have reached its high point when the gateway sequence is reduced to the gateway drug, marijuana, which has at last been proposed as gateway to licit substance use, tobacco smoking, as well (Tullis et al., 2003). The reversals of the basic GH sequence and its parallelism with ranking of the prevalences of use of respective substance categories also contradict the GH's “premise . . . that involvement in various classes of drugs is not opportunistic but follows definite pathways” (Kandel, 2002a, p. 3).
