He was also a heavy cannibis user. Of course if you're taking 25 pills a day, you do need something to take the edge off.
Apparently his neck muscles became so stiff and rigid he couldn't open his mouth for long periods. Remarkably, his MRI scans showed no anatomical changes, but his short term memory is completely shot, so much so that he doesn't know how impaired he is.
Kids, when someone offers you 25 pills every day, JUST SAY NO. It's fun to begin with, but fun doesn't last forever.