Abstract
The role played by marijuana in “precipitating” or “potentiating” the use of the more dangerous illegal drugs, particularly heroin, has received fairly detailed attention (Ball, Chambers and Ball, 1968; Glaser, Inciardi and Babst, 1969; Robins and Murphy, 1967). Although the marijuana-to-heroin equation could mean many different things empirically, probably the clearest generalization verifying the drug “progression” hypothesis would be that, on a statistical, or actuarial, basis, the marijuana user is significantly more likely to try and use heroin, as well as any other illegal dangerous drug, than is true of his peer who has never experimented with marijuana (Whitehead, 1970; Russell, 1970; Josephson, 1971; Chambers, 1971). This is especially true of the regular and frequent marijuana user; the more that one smokes marijuana, the greater is the likelihood that one will try and use any and all illegal drugs, including heroin (Goode, 1969, 1970, 1971; McGlothlin, et al., 1970; Hochman and Brill, 1971; Mirin, et al., 1971).

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