Accumulated studies have demonstrated that there are serious negative consequences of drug abuse, especially the impairment of central nervous system (CNS) function. The simple reaction time (SRT) is the simplest model of measuring the function of the CNS. The purpose of the present study is to examine whether the SRT is affected by heroin abuse and whether such drug effect, if exists, is gender related. We found significant slowing of the SRT in both male and female heroin dependent patients at 1-3 months from withdrawal. However, the SRT slowing remitted after 3 months of abstinence in heroin dependent males but not in females. Our results suggested that the SRT is slowed by heroin abuse and such slowing is gender related.