As has been stated before, if the rules are to be followed to the letter, very few of us would be allowed to post here, just by our very nature. I myself take a daily dose of a Class C Controlled Substance which, if taken by anyone other than myself, can result in 4-8 years of incarceration and a $10,000 fine. Under most cases, such a mood-altering drug would constitute sufficient transgression of the "post sober" policy to be punishable.
The spirit of the rules that are in place is clear: to provide an environment that is friendly to everyone, and to discourage certain practices that would go against that goal. In order to fulfill the above mentioned goal, a certain level of cognitive capability is generally required; thus, the use of such mood-altering substances as Zanex, Concerta, Adderall, and what-have-you, are not only not disallowed by the rule, but actually encouraged when they would benefit the person's mental or physical state. Excessive alcohol, illicit substances, or even Tylenol PM, however, are not the kinds of chemicals that promote cognitive ability.
Exceptions exist, of course, but under most circumstances, try to post when you are in a stable and clear state of mind, and ALWAYS keep your posts polite and civil. It's common decency, in a world where there is not always as much as there should be. But we can all do our part to put a little more in it