Illicit drugs is any drug that is traded on the global black market. Illicit drugs have long been a problem, there are Chinese edicts against opium smoking that were made in 1729, 1796, and 1800. And for a time the US had alcohol banned between 1920 and 1933.
Recreational drug use is the use of a drug with the intention of creating or enhancing recreational experience. Drugs commonly considered capable of recreational use include alcohol, nicotine, caffeine, and drugs within the scope of the United Nations Single Convention on Narcotic Drugs and Convention on Psychotropic Substances. Psychopharmacologist Ronald K. Siegel refers to intoxication as the 'fourth drive', arguing that the human instinct to seek mind-altering substances (psychoactive drugs) has so much force and persistence that it functions like the human desire to satisfy hunger, thirst, and the need for shelter. The concept of 'responsible drug use' is that a person can use drugs recreationally or otherwise with reduced or eliminated risk of negatively affecting other aspects of one's life or other people's lives.
Generally it's thought to diminish the effects.