As Munchies points out, he's actually mentioned this experience before, to Howard Stern of all people. (It's worth listening to the interview to hear how the Jeopardy host over-enunciates "hash brownies.") In that version of the story, he says he was in bed until the following Monday, but we may never know the truth.
He also admitted to one other experiment with pot: Years later, a friend of told him marijuana might help treat arthritis in his shoulder. "It didn't. And so I didn't continue smoking," he told Howard Stern, again using the sound, assured judgment we've come to love him for.
In case any of this changes your mind about our most moral of gameshow hosts, let's keep in mind these closing words:
"To me, drugs are highly overrated. I mean, why do it? Be confident in yourself. If you make mistakes, live with that," he explained to Howard Stern. "Why do you need to do this other stuff that's gonna take you -- where? To a different world? You're gonna be more attractive? Do you think?"