Hardcore drug users claim to be occasional users: drug use frequency underreporting

Self-reports of drug use frequency are central to treatment outcome evaluat ions, estimates of the prevalence of heavy use, estimates of treatment need , and other questions with direct relevance to drug policies. Nevertheless, surprisingly little is known about the Validity of these self-reports. Thi s study examines the accuracy of 701 frequency self-reports made by a sampl e of methadone maintenance clients. Self-report accuracy is evaluated by co mparing rates of positive urinalyses found for each case with rates that wo uld be expected had drug use occurred only as often as reported. Expected r ates of positive urinalyses are derived from conservative Monte Carlo model s of drug use for each case. This procedure reveals extensive heroin and co caine use frequency underreporting. After adjusting for frequency underrepo rting, 51% of 279 cases reporting only occasional heroin use (1-10 days in the past 30), and 22% of the 157 cases reporting occasional cocaine use, ar e found to be using these drugs with frequencies corresponding to what the Office of National Drug Control Policy defines as 'hardcore use' (more than 10 days in the past 30). Drug use frequency underreporting appears substan tial, and might constitute an important threat to the validity of some trea tment outcome evaluations, needs assessments and other analyses that rely o n drug use frequency self-reports. (C) 2000 Elsevier Science Ireland Ltd. A ll rights reserved.