Abstract

The mental illness of substance dependence or addiction is responsible for major economic, social, and personal costs. If we are to elucidate its etiology, understand its mechanisms, and eventually bring it under control, scientific investigation is essential. Research in animals and humans has enhanced our understanding of this disease through examination of genetic, neurophysiological, biochemical, and behavioral factors. But because animals cannot verbalize their subjective responses to drugs and because significant symptoms of addiction cannot be observed in non-drug-dependent humans, it is not surprising that certain investigations of substance dependence have required the participation of addicted or substance-dependent humans.