cumulative psychological dependency. In that regard, Farrington remarks that drug abusers find "that cocaine can 'fool' the brain into releasing huge amounts of dopamine at one time, producing a rush of pleasure" (Farrington, 1999, p. 20). Repeated cocaine use depletes the brain's dopamine supply--i.e., naturally available reinforcement--which aggravates the addiction, even as the psychological attraction of the brain-chemistry rush persists. Accordingly, the admission of marijuana use by high school students must be considered in conjunction with the fact that advances in cultivation between the 1970s and 1990s strengthened the concentration of marijuana's active ingredient, THC, by thirtyfold or fiftyfold, depending on which research is consulted (Leland, 1996; Lewy, 1995).
O'Brien and McLellan (1996) acknowledge the somat
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