Drawing on stress and life-course perspectives and using panel data from 1,286 south Florida young adults, we assess three critical questions regarding the role of marijuana in the "gateway hypothesis." First, does teen marijuana use independently (causally) affect subsequent use of more dangerous substances? Second, if so, does that effect apply to the abuse of other illicit substances, as defined by the DSM-IV, or only to the use of such substances? Finally, does any causal effect of teen marijuana use survive beyond adolescence, or is it a short-term effect that subsides as adolescents transition to adulthood? Our results indicate a moderate relation between early teen marijuana use and young adult abuse of other illicit substances; however, this association fades from statistical significance with adjustments for stress and life-course variables. Likewise, our findings show that any causal influence of teen marijuana use on other illicit substance use is contingent upon employment status and is short-term, subsiding entirely by the age of 21. In light of these findings, we urge U.S. drug control policymakers to consider stress and life-course approaches in their pursuit of solutions to the "drug problem." (Contains 4 tables, 2 figures, and 5 notes.)