Scientific goals: (1) To assess, cross-sectionally at baseline, differences in stress, social stability, and mental and physical health among three neighborhood-matched groups of current opioid/stimulant users, current marijuana users, and nondrug users; (2) to assess, longitudinally, mediators of 12-month changes in drug-misuse status in the same three groups; (3) to provide neighborhood-matched control groups of non-drug-using individuals, former drug users, and current drug users not seeking treatment for our ongoing environmental studies of individuals in drug treatment; (4) to assess lipid biomarkers as predictors of drug relapse with the eventual goal of developing a screening assay that will inform the personalization of treatment, (5) to explore the possible role of genetics and its interplay with environment in regards to drug use initiation, addiction, and treatment seeking among the study groups, and (6) to test blood serum and urine for the presence of several disease-associated autoantibodies, including ANCA, ANA, and antiophospholipid antibodies, in relation to the presence of levamisole (a common adulterant in cocaine); (7) to assess EMA reports of drug use and psychosocial stress as well as real-time environmental risk exposure in a non-treatment seeking and/or nondrug using population and compare to our ongoing environmental studies of individuals in drug treatment,