Drug abuse is considered to be a public health problem that is growing rapidly, especially among youths, who make up about half of the total population in Mexico. IRSD is an information system that reports event, based on two month-long, cross-sectional evaluations made each June and November. Data for IRSD are gathered by means of a questionnaire called the individual report on drug abuse. Illicit drug users complete these reports upon admission to health and criminal justice facilities and institutions in Mexico City during the evaluation periods. Analysis of the findings has shown that most users are from the lower and middle socioeconomic levels of the population. However, these groups are the main ones who go to the facilities taking part in IRSD, as users from upper socioeconomic groups tend to go to private facilities, which adds to the element of secrecy surrounding drug abuse in Mexico. Tables and 17 references. (Author abstract modified)