The little I know – please provide your sources.
From R’ Elyashiv: It’s assur to *start* smoking (because sakana), but once someone is addicted, it is a tzorech for him so then it is not assur.
Background: The Noda B’yehuda was asked if hunting is mutar; he said no because there are many accidents, so it’s a sakana. But, if it is a tzorech for someone (i.e. his parnasa) then it is no longer assur. So too, someone that is addicted to smoking has a tzorech to smoke so it’s muttar.