Consistent trends were also documented with respect to the period of risk for initiation of drug use. In most countries, the period of risk for initiation of use was heavily concentrated in the period from the mid to late teenage years; there was a slightly older and more extended period of risk for illegal drugs compared to legal drugs. Analyses of possible intercohort differences in risk of initiation suggested not only that the levels of illegal drug use were higher, but also that in more recent cohorts, the period of risk was extending further into adulthood. This extension of the period of risk has implications for drug use prevention efforts, which often focus upon adolescents and do not actively target young adults. Clearly, for illegal drugs, there continues to be a window of risk of initiation of illegal drug use that persists well beyond that of most commonly targeted ages.
