To examine the consequences of adolescent drug use on the psychosocial and health functioning of young adults, we followed up 1004 young men and women from age 15 or 16 years to age 25 years. The use of four different classes of drugs was examined: cigarettes, alcohol, marijuana, and other illicit drugs. Twenty outcomes were examined, including continuity of participation in work and in family roles, level of education, delinquent activities, self-reported health and psychological symptoms, and use of five drug classes in early adulthood (including prescribed psychoactive medications). The effects of marijuana and of other illicit drugs could not be disentangled, so these drugs were treated as a single class. Controlling for initial individual differences in adolescence, use of the three major drug classes between adolescence and early adulthood affected most of the outcomes examined; most strongly continued use of the same substance. Unique drug effects included those of illicit drugs on increased delinquency, unemployment, divorce, and abortions, and of cigarettes on lowered psychological mood. Illicit drugs predicted drug-related health problems, whereas cigarette use predicted increased breathing difficulties.