I'm thinking this is probably "Inside John Barth" by William S. Stuart as per the answer to this question.
late 20’s man is hit by several micrometeorites, taken to the hospital, and “looks like you were hit by a shotgun".
"Buckshot, I suppose. What was it you just hacked out of me?"
"Hah!" He passed the bottle back to Uncle John. "Not like any buckshot I ever saw. Little balls, or shells of metallic stuff all right. But not lead. Peculiar. M-mph. You know what, boy?"
"You're mighty liberal with the iodine, I know that. What else?"
"You say you saw a big flash of light. Come to think on it, I saw a streak of light up the mountainside about that same time. I was out on the porch. You know, boy, I believe you got something to feel right set up about. I believe you been hit by a meteor. If it weren't—ha-ha—pieces of one of them flying saucers you read about."
Aliens set up a symbiotic relationship. Protagonist tried drinking heavily to quiet the voices. From the alien perspective, it was a yearlong party, instead of just one night. They come to an accommodation of 1 drink every now and then.
Another thing was my approach to—or retreat from—drinking. Not that I ever was a real rummy, but I hadn't been one to drag my feet at a party. Now I got so moderate it hardly seemed worth bothering with at all. I could only take three or four drinks, and that only about once a week. The first time I had that feeling I should quit after four, I tried just one—or two—more. At the first sip of number five, I thought the top of my head would blast off. Four was the limit. Rigidly enforced.
All that winter, things like that kept coming up. I couldn't drink more than so much coffee. Had to take it easy on smoking. Gave up ice skating—all of a sudden the cold bothered me. Stay up late nights and chase around? No more; I could hardly hold my eyes open after ten.
AND all they wanted for me were such fine things as good health, long life, contentment. Contentment, sure. Continued irritation—a sour disposition resulting in excess flow of bile—did not provide just the sort of environment in which they cared to bring up the kiddies. Smoking? No. It wasn't healthy. Alcohol? Well, they were willing to declare a national holiday now and then. Within reason.
Which, as I already knew, meant two to four shots once or twice a week.
It’s possible that the aliens encourage the protagonist to engage in many one night stands, to help spread the aliens.
AS they had explained it, they were prepared to be tolerant about my—ah—relations with women as long as I was "reasonable" in my selection. Come to find out, they were prepared to be not just tolerant but insistent—and very selective.
Well, I thought myself that I had turned in a pretty outstanding performance, but I hadn't expected such applause. "It is a first step, a splendid beginning! A fully equipped, well-armed expedition will have the place settled, under cultivation and reasonably civilized inside of a day or two, your time. It will be simple for them. So much more so than in your case—since we now know precisely what to expect."
And as regards drinking heavily to remove the voices:
"Yes. At what we pumped from your stomach. And found in the girl's. Liquor, lots of that—but then, why aspirin? Barbiturates we expect. Roach pellets are not unusual. But aureomycin? Tranquilizers? Bufferin? Vitamin B complex, vitamin C—and, finally, half a dozen highly questionable contraceptive pills? Good Lord, man!"
Now what? What should I do? I turned, as always, inward for advice and instructions. "Folks! Why didn't you stop me? Why did you let me do it? And now—what shall I do? Answer me, I say. Answer!"
There was only an emptiness. It was a hollow, aching sensation. It seemed to me I could hear my questions echoing inside me with a lonely sound.
I was alone. For the first time in nearly ten years, I was truly alone, with no one to turn to.