Quoted from adamzero

For George the drug was simply a vehicle.  For John, an end in itself.  Both sought annihilation of the ego, but John had nothing left once he'd annihilated his.  So he just turned to another drug--heroin, cocaine, alcohol.  George integrated his acid experiences into a new psyche that could admit it wasn't the center of the universe.  John, for all his causes, seemed to remain self-centered to the end.