Talent (sports, film, music...doesn't matter) who has an entourage is more likely than not to die young of a drug overdose.
From what I've read it's the need to feed that entourage that brings the downfall. The need to keep the income high, the need to perform whether your body wants to or not. The pressure to have another hit or your career is over.
Bill Bruford wrote a little about this in his book, what he's seen brushing up against the big time a couple times, plus the transformation he saw in Phil Collins, going from moderately successful in the 70's to The Big Thing in the 80's. Bill Bruford survived and thrived by just getting out of the situations when they rose (quitting Yes as they hit the big time.)
Obviously Whitney never could cope.