My two cents (and sometimes yours) about Jewish identity, atheism, multiculturalism and related matters.
No, and no.That is, smoking is not considered assur, and though some have argued that it should be forbidden under the general law of not doing dangerous things, that doesn’t seem to be the consensus. When I was in high school smoking was against school rules, and guys would be fined if they were caught with cigarettes, but no one ever thought to claim that it was assur. And this is a place where someone once said that water fights were assur because the rosh yeshiva had said not to have water fights, and he had daas torah… but I digress.And no, as far as I know, no one has thought to put a hechsher on cigarettes. Maybe a lucrative new market?
Smoking was once assumed to be healthy and widely accepted to be an aid to digestion, thus permissible halachically. Some halachic authorities now claim that smoking is assur. There are also some roshei yeshivot who tell students "you can't learn here if you smoke". But there is no across the board prohibition on smoking based on that catchall used for other dangerous activities "u'shmartem es nafshoseichem" (you shall guard your souls). The reason? Orthodoxy has largely abandoned the notion that halacha can change with new knowledge. It's tied to the widespread belief among chareidim that chazal and later rabbinic authorities were infallible.
Smoking was at one point quite common in the yeshiva world.Rabbi Moshe Feinstein wrote that it was not forbidden, as many gedolim (great Torah scholars) had been smokers and since "G-d protects the simple". He was considered to be a "Gadol" (big, authoritative rabbi) in America.More recently, I have seen respected Orthodox opinions that smoking is now considered to be forbidden, because it endangers health. Much more is known today about the dangers of smoking than when Rabbi Feinstein wrote his ruling, there is more public awareness and smoking is becoming less common - all of which represent changes to the basic facts upon which the previous ruling was based. People can no longer be considered "simple" in this area.