Cross-sectional and longitudinal causal analyses were carried out on a longitudinal cohort of 400 employed adult males. By age 35, there were no cumulative effects of the use of illicit drugs on wages. Specification of the relationships at various stages of the life cycle reveals that the effects of illicit drug use are positive in the early stages of labor force participation (by the late twenties) but negative in later stages (by the mid-thirties). The negative impact of drug use on earnings appears to take more than a decade to manifest itself and is reflected in lower rates of earnings growth. A labor market theory of life-cycle compensation contracts and investments in training, and the differential impact that different types of job changes have in the short and the long run among users and nonusers may provide a partial accounting of the processes underlying the observed opposite relationships between drug use and earnings at different age periods. The study findings highlight the importance of adopting a life-span perspective. Tables, figures, appendixes, references