I've always kind of theorized that after the Hiatus, Watson was so much more afraid of losing Holmes that he became a lot more forceful in his warnings. Like, maybe he threatened to walk out and never see Holmes again if he didn't let Watson help him quit.

Somehow, I can't really see Holmes deciding that he might not be perfectly in control of his health as long as he took it irregularly enough to not get seriously addicted. And he'd totally be the type who would always be careful enough to not overdose.

(I would LOVE recs for good withdrawal-fics, btw. Anyone?)