Background. The reasons for initiation and continuation of use of illicit substances are multifactorial; however, some individuals appear resistant to both. One set of determinants lies in the environment. In ongoing studies, we are examining environmental concomitants of behavior in individuals in drug treatment. In this study, we will examine environmental factors that may impact initiation, addiction, and treatment seeking among the greater population at large (non-drug-users, former drug users, current opioid/stimulant users seeking treatment, current opioid/stimulant users not seeking treatment, and current marijuana users). Using the same participants, we will also investigate lipid biomarkers as predictors of relapse; this portion of the study will be a collaboration with preclinical investigators who have identified a possible lipid fingerprint of cocaine sensitization. The results could inform prevention efforts, enhance treatment interventions, and improve substance use outcomes.