Basically, Leary grew to prominence but his scientific methods were often faulty and he turned to mysticism. He became a cultural advocate, not a scientific one. But his ties to psychedelic research it a bad name and made it much more difficult for people to get their hands on these drugs for the purposes of actual research. Eventually, mostly due to backlash against Leary, these substances were prohibited from research use for several decades. It was only in the late 90s that we began to pick up the pieces.