Timing of alcohol and other drug use

Many Americans who drink alcohol are polydrug users--that is, they also use other psychoactive drugs, such as nicotine, pharmaceuticals, cannabis, and other illicit substances. Polydrug use is a general term that describes a wide variety of substance use behaviors. Different types of polydrug use can be described with regard to the timing of the ingestion of multiple substances. Concurrent polydrug use (CPU) is the use of two or more substances within a given time period, such as a month or a year. Simultaneous polydrug use (SPU) is the use of two or more substances in combination (i.e., at the same time or in temporal proximity) (Grant and Harford 1990a). Thus, although all simultaneous polydrug users are, by definition, concurrent users, concurrent users may or may not be simultaneous users. This article describes the functions of SPU for substance users, as well as the measurement, prevalence, patterns, and consequences of SPU.