I can give you some harmful side effects. This is a sentence about addiction from "Infinite Jest" by David Foster Wallace.[1]

Because if you sit up front and listen hard, all the speakers' stories of decline and fall and surrender are basically alike, and like your own: fun with the Substance, then very gradually less fun, then significantly less fun because of the blackouts you suddenly come out of on the highway going 145 kph with companions you do not know, nights you awake from in unfamiliar bedding next to somebody who doesn't even resemble any known sort of mammal, three-day blackouts you come out of and have to buy a newspaper to even know what town you're in; yes gradually less and less actual fun but with some physical need for the Substance, now, instead of the former voluntary fun; then at some point just very little fun at all, combined with terribly daily hand-trembling need, then dread, anxiety, irrational phobias, dim siren-like memories of fun, trouble with assorted authorities, knee-buckling headaches, mild seizures, and the litany of what Boston AA calls Losses -
... (here DFW interpolates part of a monologue from an AA speaker)
-then less mild seizures, D.T.s during attempts to taper off too fast, introduction to subjective bugs and rodents, then one more binge and more formicative bugs; then eventually a terrible acknowledgment that some line has been undeniably crossed, and fist-at-the-sky, as-God-is-my-witness vows to buckle down and lick this thing for good, to quit for all time, then maybe a few white-knuckled days of initial success, then a slip, then more pledges, clock-watching, baroque self-regulations, repeated slips back into the Substance's relief after like two days' abstinence, ghastly hangovers, head-flattening guilt and self-disgust, superstructures of additional self-regulations (e.g. not before 0900h, not on a worknight, only when the moon is waxing, only in the company of Swedes) which also fail -
...
-then unbelievable psychic pain, a kind of peritonitis of the soul, psychic agony, fear of impending insanity (why can't I quit if I so want to quit, unless I'm insane?), appearances at hospital detoxes and rehabs, domestic strife, financial free-fall, eventual domestic Losses -
...
-then vocational ultimatums, unemployability, financial ruin, pancreatitis, overwhelming guilt, bloody vomiting, cirrhotic neuralgia, incontinence, neuropathy, nephritis, black depressions, searing pain, with the Substance affording increasingly brief periods of relief; then finally no relief available anywhere at all; finally it's impossible to freeze what you feel like, being this way; and now you hate the Substance, hate it, but you still find yourself unable to stop doing it, the Substance, you find you really want to stop more than anything on earth and it's no fun doing it anymore and you can't believe you ever liked doing it and but you still can't stop, it's like you're totally fucking bats, it's like there's two yous; and when you'd sell your own dear Mum to stop and still, you find, can't stop, then the last layer of jolly friendly mask comes off your old friend the Substance, it's midnight now and all the masks come off, and you all of a sudden see the Substance as it really is, for the first time you see the Disease as it really is, really has been all this time, you look in the mirror at midnight and see what owns you, what's become what you are -
...
-and then you're in serious trouble, very serious trouble, and you know it, finally, deadly serious trouble, because this Substance you thought was your one true friend, that you gave up all for, gladly, that for so long gave you relief from the pain of the Losses your love of that relief caused, your mother and lover and god and compadre, has finally removed its smily-face mask to reveal centerless eyes and a ravening maw, and canines down to here, it's the Face In The Floor, the grinning root-white face of your worst nightmares, and the face is your own face in the mirror, now, it's you, the Substance has devoured or replaced and become you, and the puke-, drool-, and Substance-crusted T-shirt you've both worn for weeks now gets torn off and you stand there looking and in the root-white chest where your heart (given away to It) should be beating, in its exposed chest's center and centerless eyes is just a lightless hole, more teeth, and a beckoning taloned hand dangling something irresistible, and now you see you've been had, screwed royal, stripped and fucked and tossed to the side like some stuffed toy to lie for all time in the posture you land in.

[1]: http://www.reddit.com/r/books/comments/f8me0/favourite_sente...