Among those factors, the most important direct influence on drug use is that of the peer cluster: 'gangs,' best friends, or couples. Other psychosocial characteristics, however, set the stage for this involvement with drug-using peer clusters. Social characteristics that influence drug use in this way include the community, socioeconomic status, neighborhood environments, family, religion, and the school. Psychological characteristics tend to have only low correlations with drug use, but there is some influence on peer clusters from traits such as self-esteem, depression, anxiety, and introversion, particularly when these lead to anger. Implications for prevention and treatment are considered. (Author abstract)