Yep. He was using the time-honored “start with insignificant dose; if no effects, double it; rinse and repeat until mild effects begin to occur, then go from there” method of self-experimentation. (Has a formal name, I think, but memory fades…)
So he took what he figured would be an insignificant whole-body dose - half a milligram. After awhile, when nothing seemed to be happening, he decided to bicycle home.
Half a milligram is 500 micrograms.
Five Hundred MICS of lab-pure LSD-25.
Wheeeeeeee!