Individual differences in acute effects of drugs in humans: their relevance to risk for abuse.

It is known that individuals differ in their likelihood of becoming drug abusers. Many people never take any drugs at all, even on a single occasion. Of those who take drugs at least once, only a small number go on to use the drugs on a regular basis, and even fewer go on to use them in excessive quantities or abusive patterns. The differences in numbers of individuals who have ever tried drugs and those who become regular users is roughly illustrated by data from a national household survey (National Institute on Drug Abuse 1992): 37 percent of U.S. adults reported having used an illicit drug at least once in their lives, while only 6.3 percent report having used an illicit drug in the past month. “Illicit drug” here includes marijuana, nonmedical use of psychotherapeutics, inhalants, cocaine, hallucinogens, or heroin. Similarly, in 1993, 43 percent of U.S. high school students reported having tried an illicit drug at least once in their lives, while only 18 percent used any drugs in the past month (National Institute on Drug Abuse 1994). Many individuals limit their use to an initial sampling of the drug. Other individuals become occasional users, but use the drugs in moderation without developing any problems of abuse or dependence. However, a small but significant proportion of young individuals appears to progress rather rapidly (i.e., in their late teens and early twenties) to excessive use, and continue to use drugs despite harmful consequences. Why some individuals and not others are susceptible to drug or alcohol abuse is unclear. Some researchers have investigated risk factors through epidemiological or longitudinal studies designed to detect predictors and correlates of heavy drug use (see Tarter, this volume). Other researchers have used laboratorybased procedures to investigate individual differences in acute responses to drugs. This chapter will focus on a series of studies that used the latter approach to examine individual differences in response to acute doses of benzodiazepines.