Patterns of onset and cessation of drug use over the early part of the life course.

This study uses retrospective drug use histories to examine the timing of drug use behavior among young people participating in a large random probability survey of residents of the province of Ontario, Canada. Results reveal that the major risk period for initiation into alcohol, tobacco, and most illicit drugs begins around age 12 and is mostly over by age 22. For most drugs, peak periods of risk of initiation occur in the age range 15 to 19. For all categories of illicit drugs, results reveal high quit rates in the first few years of use followed by a sharp decline. Differences by gender reveal higher rates of onset for males for most drugs. Male drug users are significantly less likely than female users to quit using a drug. Results are discussed in terms of their implications for the development of primary prevention and early intervention programs for adolescents and young adults.