n-acetylcysteine
Don't know the time where you are, but get to a nutrition store and buy some if you can. If taken, preferably before 12 hours post Tylenol, and it will help up to 24 hours post Tylenol, but faster is better, it will stop the toxic effects of Tylenol. In the ER, someone can come in having taking 30 GRAMS of Tylenol, as long as it's within 12 hours, IV n-acetylcysteine and they will have no liver damage and be 100% fine. 12-24 hours will save their lives, but they will get liver damage. After 24 hours they will die in agony within 3 days without a liver transplant, which is about a 1 in a million chance in that time frame. And there are no signs/symptoms until 24 hours.
Now the amount you took, assuming you don't have liver problems already, you should be fine with no issues. But n-acetylcysteine (NAC) isn't bad to have on hand if you do DXM a lot and mess up again (hopefully you've learned your lessons to CHECK THE BOTTLE, and don't think you can just use NAC and then use DXM with Tylenol, you will hurt yourself, possibly fatally.)
I should say I don't know how well oral NAC works in relation to the IV NAC in the hospital, so for dosage and effectiveness you'd need to research, but if you can get some quickly and it hasn't been 24 hours you might want to grab a bottle and just take some (It's safe even at dosages higher than the bottle will say.) AND NO, having NAC doesn't mean you can start using DXM with Tylenol in it all the time, Tylenol overdoses big enough to kill your liver are one of the more horrible ways to die. Especially since it's usually related to a suicide attempt, when the patient will then change their mind and want to live after a few hours or usually minutes, but because there are no symptoms they don't go to a doctor. By the time they have symptoms, want to live again, and they go to a hospital, they're already doomed to die within 3 days, in physical and obvious psychological agony.
I made my post scarier than needed. With your dosage, one time (and assuming you have no chronic liver problems) you will be 100% fine. But Tylenol OD's are truly an awful death, so I was being a bit dramatic perhaps. From now on PAY ATTENTION, and if you get into the 6+ gram range get to an ER even though you will feel fine. Oh, and I'm not trying to act holier than thou or anything. I've taken that much Tylenol with hydrocodone before when I was younger/dumber. I just don't want you or anyone reading to not realize the seriousness of Tylenol OD's, and that they need to be acted on EVEN WITHOUT SYMPTOMS. Your post makes me think you know all/most of this already. But seriously, if you think you might ever mess up, or even if you're getting close to the maximum allowed (like 3 grams in one dose is 2 grams too much, etc.), take some NAC after it and you'll be better off.
Peace dude
