Results found significant gender differences between men's and women's changing likelihood of illicit drug use over the life course. In particular, models of within-person change show that although getting married may be an important hook for change for men, it has little impact on women's illicit drug use. Instead, the strength and importance of a relationship with a significant other is particularly well suited to inform social policy by pointing out significant hooks for change. Results imply that policy use might consider gendered interventions. For example, a social policy strengthening relationships appears to be particularly important for reducing women's illicit drug use. For men, perhaps the emphasis would be better placed on increasing the appeal and influence of employment. Because several factors were found that had different effects on men's and women's substance use, it is suggested that social policy and criminological theory put forth more effort into understanding how gender moderates the effects of various social and economic influences. Data were collected from the National Youth Survey (NYS) in which a nationally representative probability sample of 1,725 youth, aged 11 to 17 years, were interviewed in 1976 and followed-up annually through 1980, and again in 1983 and 1986. Table, appendix, notes, and references