Is It OK to Smoke Marijuana On Yom Kippur?
Yom Kippur is more strict than Shabbat in most cases (including today)
It is debatable whether smoking marijuana is allowed on other holidays. You would have to ask your Posek (the rabbi whose decisions you follow)
With Marijuana you have the added issue that there is a Jewish rule that you must keep the laws of the land unless they expressly contradict the Jewish covenant.
Thus, it is likely that Marijuana in the US is prohibited unless you have a medical Marijuana prescription for the state you are in.
Finally, there is the question of health impact. When rabbis in the 20th century were asked why they do not prohibit tobacco, they said that since the science was not definite, they could not rabbinicaly prohibit it.
It is arguable that if a rabbi was re-evaluating the matter of tobacco today, he would have to say it is prohibited because it is “poison”. My assumption is that Marijuana today is in the status of dilatability — if you believe the science that it has long-term negative impacts, then you would be prohibited from using it since you are not allowed to poison yourself.
Anything detrimental to one’s health, and certainly anything illegal, should be avoided all year long according to many answers we found. As to the theoretical issue of smoking on a fast day, on Yom Kippur the issue is most likely prohibited because of the fire involved. Anyone else care to chime in?