That entirely depends on how much the addict wants to stop indulging in his or her particular vice of choice.

[He shrugs, not at all phased by the subject matter.]

Some people don't want to stop their addiction, some people lie to themselves that they aren't strong enough but they have just not found something they care about more than the continuing endorphin rush the vice gives them. All addiction can be overcome, even one centuries in the making. Perhaps three centuries, at an estimate.