Sugar pills...
...laced with LSD.
I left that part out on purpose. I didn't want to have to be the one to tell him that he is the only one on the forums and that everyone else has been a figment of his imagination. He himself is a construct of his own imagination much like everyone else he has been talking too.
But we cannot tell him his own name, as his mind might implode upon itself and bring our cozy little world to a very violent and abrupt end.