Recreational drug use is the use of prescription and non-prescription drugs for the purpose of altering one's mental state. Recreational drug use can be addictive, deadly and in many cases violates the law.
Enhancing drugs are also used for recreational purposes. It's very difficult to separate these two uses, but there are important differences between recreational use of enhancing drugs and use of purely enhancing drugs. The most popular enhancing-and-recreational drug is caffeine, but its used for enhancement much more often than for recreation.
See also: Drug