I think doctors sequenced his genome a couple years back and found out he's got mutations that are linked to drug resistance of some type. As in, the type that has prevented him from dying like 50 times in his life, and not that he can't get high. He still fucked up his brain real hard from drug abuse, but he's a scientific marvel that he lasted so long.

It's sort of like once every million or so people you got that guy who smokes like a chimney and loves alcohol and lives cancer-free until he's 95 and then just dies of a heart attack.