how long can opened, unrefrigerated beer last before it will make you sick?!

Best Answer - Chosen by Voters

If left out overninght, beer loses its carbonation. Then it is flat and loses its beer taste.

The exception to this is Bud, Millers, Coors, and lite beers which never had a beer taste.
When they go flat. it's like drinking stale water.

For other beers (Guiness, Newcastle Brown Ale, Belhaven Scotch Ale), they too
become flat, but still have taste.

None of this will make you sick unless some bad bacteria got into them.

The solution is to think of all the poor children in Africa who go to bed sober and
drink all of your beer.

It will taste bad before it "makes you ill." The carbonation will go out of it making it flat after just a couple of hours. Warm, flat beer would probably taste pretty icky. You could probably leave it out for a fair amount of time before a bunch of bacteria grows in it, but who would want to? Also, if it is open, alcohol evaporates quicker than water, so it will lose that, too. Just don't do it.

If it's Bud, Millers, or Coors, it was really not good beer anyway.

Otherwise about six months.