>4 hrs, overnight or more) or in smoking frequency between the groups (P>0.54 t-test). Nineteen cocaine subjects met DSM-IV diagnosis for cocaine dependence or abuse, and had at least a 12-month (4 days/week for all but one subject) history of cocaine use (predominantly by the smoked route). Two cocaine dependent subjects also met diagnosis for cannabis or alcohol abuse. Two subjects had histories of past alcohol dependence. Seventeen of the cocaine subjects had a positive urine toxicology screen for cocaine on the day of the study, indicating that they used cocaine during the prior 72 hours. The urine toxicology screen was negative for the remaining three cocaine subjects and for all control subjects.
