Incidentally, I had a lecture about this earlier today; my prof is an expert on addiction and was one of the people vetted by tobacco companies to prove that nicotine wasn't the cause of cigarette addiction a few decades ago.
He mentioned how since tobacco was linked to cancer, the numbers of smokers in the US have dropped by half. However, that's just the US alone, and that's over several decades, so the correlation does not necessarily imply causation. In other countries, smoking rates are just as high as ever, and they assuredly know that smoking leads to cancer.
That said, I assume that smoking rates are more of a societal thing, and a revelation of the side effects might drop smoking rates slightly, but not a great deal.