Having done that for awhile once? It basically is, and that is the typically OTC recommended dose.
They also sell 1-gram extra-strength Tylenol pills OTC, but that's a very high dose for an average person. And what do you know, acetaminophen is the leading cause of acute liver failure in the US.
That typical OTC doses for a common antihistamine ARE probably equivalent in impairment to being legally drunk for most people is mine?