This term implies the purposeful choice and use of a psychoactive substance to control, treat or diminish a mental disorder, symptom, or personality trait even when the drug use is disordered.
It is the way of John Barleycorn. When good fortune comes, they drink. When they have no fortune they drink to the hope of good fortune. If fortune be ill, they drink to forget it. If they meet a friend, they drink. If they quarrel with a friend and lose him, they drink. If their lovemaking be crowned with success, they are so happy they needs must drink. If they be jilted, they drink for the contrary reason. And if they haven't anything to do at all, why they take a drink, secure in the knowledge that when they have taken a sufficient number of drinks the maggots will start crawling in their brain and they will have their hands full with things to do. When they are sober they want to drink; and when they have drunk they want to drink more.* -- Jack London
A madman who takes hashish contracts a new madness that puts the other to flight; but once the intoxication has run its course, true madness, which is the madman's norm, resumes dominion, just as health and reason do in us. -- Charles Baudelaire