The use of psychoactive substances is popularly believed to loosen sexual inhibitions and contribute to increased sexual activity. However, the actual direct and indirect effects of alcohol and drugs on sexual function are still not fully understood. This article provides a new critical review of the research on the impact on male and female sexual function of psychoactive drugs including alcohol, nicotine, and illicit drugs. The authors consider the effects of both acute and chronic use and review findings from controlled laboratory studies as well as survey and interview research. Research on the impact of substance use and abuse on human sexual function has some limitations due to small and nongeneralizable samples, lack of controlled research design or comparison groups, reliance on self-reported data, or failure to specify or control for dosage effects, expectancies, social effects, and multiple substance use. The lack of controls on physiological, psychological, environmental and cultural factors that could alter the relationship between substance use and sexual function also make it difficult to draw conclusions about direct causal mechanisms. Despite these limitations, this review suggests that chronic alcohol and drug abuse have clear deleterious affects on sexual functioning for many individuals.