my estimate would bigger than others and I would put it at 30-50years.
I take smoking as a cautionary tale, in the beginning it was pushed as not just a recreational thing but a healthy activity that bring benefits with papers published to sing praises about it. my parents were even nudged by their teachers/doctors/etc when they were young to try smoking.
now we all know that smoking is beyond bad and all that early "research" was just people paid off by big companies to promote it.