“[v]ery few individuals who have tried cocaine and heroin have not already used marijuana; the majority have previously used alcohol or tobacco” (Kandel, 2003, p. 482), the conclusion is drawn (Kandel, 2002a) that “there is a progressive and hierarchical sequence of stages of drug use that begins with tobacco or alcohol, two classes of drugs that are legal, and proceeds to marijuana, and from marijuana to other illicit drugs, such as cocaine, metamphetamines [sic], and heroin” (p. 3).
