Aims: To examine whether male-female differences in rates of drug use could be traced back to differences in rates of exposure to initial opportunities to try drugs, rather than to sex differences in the probability of making a transition to use, once opportunity has occurred.
Design: Cross-sectional sample survey research with nationally representative samples and retrospective assessments.
Setting: United States, 1979-94.
Participants: Respondents were 131,226 residents aged 12 years and older, recruited for the National Household Surveys on Drug Abuse by multi-stage probability sampling at nine time points.
Measurements: Estimated proportion of males and females with an opportunity to use marijuana, cocaine, hallucinogens and heroin; proportions reporting use among those having an opportunity to use each drug; proportion making a "rapid transition" from initial opportunity to initial use.
Findings: For each survey year, males were more likely than females to have an initial opportunity to use drugs. However, few male-female differences were observed in the probability of making a transition into drug use, once an opportunity had occurred.
Conclusions: Previously documented male excess in rates of drug use may be due to greater male exposure to opportunities to try drugs, rather than to greater chance of progressing from initial opportunity to actual use. This suggests that sex differences in drug involvement emerge early in the process. Implications of these findings are discussed in relation to the epidemiology and prevention of drug use, and future research on sex differences in drug involvement.