Baudelaire makes the point in his essay, "Wine and Hashish: Compared as Means for the Multiplication of the Personality," that a dictionary tells you nothing about wine. (He quotes Lavater: "May God preserve those he loves from profitless reading!") You can learn the meaning of the word "wine," but you will learn nothing about the meaning of the thing itself.
Well, no need to do drugs yourself when you can refer to the decadents' accounts. Gautier describes the effects, in "Hashish," as occurring in three waves; here is his impression of the second, arguably most intense, phase:
Not more than half an hour had passed before I succumbed once more to the hashish. On this occasion, the vision was of greater complexity and even more astonishing. In an atmosphere of confused light, there fluttered a never-ending swarm of myriads of butterflies, their wings rustling like fans. Giant flowers with crystal cups, enormous hollyhocks, lilies of gold and silver, shot up and spread about me with detonations like those of fireworks. My sense of hearing had become abnormally acute. I could hear the very sounds of the colours. Sounds which were green, red, blue or yellow, reached my ears in perfectly distinct waves. An overturned glass, the creaking of an armchair, a whispered word, vibrated and echoed within me like peals of thunder. My own voice seemed so loud that I did not dare speak for fear of shattering the walls or of myself exploding like a bomb; more than 500 clocks were singing out the hour to me in their fluting, brazen or silvery voices. Any object brushed against would emit the notes of musical glasses or an Aeolian harp. I swam in an ocean of sonority in which there floated, like an island of light, motifs from Lucia or the Barber. Never had such beatitude flooded me with its waves: I had so melted into the indefinable, I was so absent, so free from myself (that detestable witness ever dogging one's footsteps) that I realized for the first time what might be the way of life of elemental spirits, of angels, and of souls separated from their bodies. I was like a sponge in the midst of the ocean: at every moment floods of happiness penetrated me, entering and leaving by my pores for I had become permeable and, down to the minutest capillary vessel, my whole being had been transfused by the colour of the fantastic medium into which I had been plunged. Sound, perfume and light came to me through multitudes of channels as delicate as hairs through which I could hear the magnetic current whistling. According to my sense of time, this state lasted some three hundred years, for the sensations came in such numbers and so thickly that true appreciation of time was impossible. The attack passed and I saw that it had lasted a quarter of an hour.
Gautier's entries appear to blend fact with fantasy; they bear the typical dreamlike quality of his stories.
It seems that in the mid-1800s, inspiration was a very serious concern, to artists and philophers, but also to scientists. Thinkers of various persuasions would engage in drug behaviour not in pure debauchery but as part of a thorough study of those elements that contribute to an aesthetic.
Baudelaire's account attempts to be a more objective account of the effects of wine versus hashish; it carries an authoritative tone and is sprinkled with anecdotes. He ultimiately comes down on the side of wine: it is profoundly humane, whereas hashish is anti-social (and in particular warns those whose "temperament is confined to the splenetic" against it).
Why ingest any substance at all when you can exult in such poetry as these men have to offer!