I am appalled at the azus of some people that claim that Rav Moshe ZT”L was mattir smoking tobacco. Chas veshalom! The question posed, relevant to the extent of scientific knowledge at the time, was whether giving a match to someone to light up was considered ???? ??? ?? ??? ?????. He felt that the evidence to go that far was not there (in approximately 1962). But he clearly stated that those not smoking should not begin, and those who already were smokers should stop. A link to the tshuva above should help identify what Rav Moshe really said. I also heard from others who quoted Rav Moshe as having stated (verbally, not known if in writing) that smoking was clearly assur.
There is a sefer bearing a large number of haskamos of well known, universally recognized Gedolei Hador in which the subject is discussed in full length, referenced with quotes from poskim (not anonymous commenters like me). ???? ??? ????? – ?????? ??????. There was a prior sefer that addressed this: ??? ??? ??? – ??’ ?? ?????? bearing haskomos from Rav Shteinman ????”? and Rav Shlomo Zalman Auerbach ZT”L. It contains tshuvos from a wide range of Poskei Hador. There are countless other references, but the comment feature here would be overwhelmed by a catalogue of all these references. Just try the above two. Then we’ll deal with smoke by a substance undeniably far more serious that tobacco.
As for medicinal marijuana, and the interest of having a hechsher available, there is a simple comment. Medicines all involve some form of toxicity, making them effective at “killing the disease”. It becomes a highly professional judgment call if the negative aspect of the medicine is worse than the potential benefit or vice versa. It would be wise to view all medications as a subject requiring a balance between the benefits versus the risks. Same goes for marijauna. Taking it casually is not different from ingesting a medication used for chemotherapy for cancer just for fun. Stupid, dangerous, and against halacha.