We assess whether in utero exposure to legalized abortion in the early 1970's affected individuals' propensities to use controlled substances as adolescents. We exploit the fact that some states legalized abortion before national legalization in 1973 to compare differences in substance use for adolescents across birth cohorts in different states. We find that persons exposed to early legalization were, on average, much less likely to use controlled substances. We also assess how substance use varies with state level birth rates and abortion ratios. Overall, our results suggest that legalization lowered substance use because of the selective use of abortion by relatively disadvantaged women.