There is an established and possibly increasing trend for recreational drug users to use two or more drugs in combination to achieve a particular effect. Analogously, a large number of persons has an "addiction" to the combined effect of two or more drugs. Recreational drug use is the use of psychoactive drugs for recreational rather than for working or for medical or spiritual purposes, although the distinction is not always clear. ... A psychoactive drug or psychotropic substance is a chemical that alters brain function, resulting in temporary changes in perception, mood, consciousness, or behavior. ... Drug addiction, or dependency is the compulsive use of drugs, to the point where the user has no effective choice but to continue use. ...

There is a great body of testimonial and scientific evidence to suggest that a majority of recreational drug users are polydrug users.

Polydrug use may occur because the user's preferred drug is unavailable (or too expensive) at the time.

There are many popular drug combinations, including, but not limited to; marijuana and alcohol, benzodiazepines and alcohol, cocaine and heroin, & ecstasy and methamphetamine.

Polydrug use carries with it more risk than use of a single drug, due to an increase in side effects, and unique pharmacological interactions.

The phenomenon is apparently the subject of established academic literature (e.g., Scholey AB, Parrott AC, Buchanan T, Heffernan TM, Ling J, Rodgers J (2004). "Increased intensity of Ecstasy and polydrug use in the more experienced Ecstasy/MDMA users: a WWW study." Addictive Behaviors, 29, 743-752).