George Carlin, one of the most prolific and revolutionary comedians of the 20th century, experienced a severe shift in consciousness some time in the late 1960s. He began to experiment with LSD and mescalin and realized he was feeding an unhealthy system.
He quickly began to change styles and, instead of doing comedy for the older, stodgier, generation, began to play colleges for the young people. His entrance into the mainstream culture and popularity was preceded by magnificent drug use.
His voice still rings true today. The power of these drugs and the value they hold (even in single or limited uses) is unquestionable to those that have used them in the right setting and dose. MIT and Johns Hopkins have even begun large-scale studies on the effect they have on the human brain.
Much is yet to be found, but because of people like George Carlin, we are coming out of the dark age.