According to Jewish law, is one allowed to smoke drugs? (I mean not regularly)
This question was addressed by Rabbi Moshe Feinstein in his book Responsa Igrot Moshe Vol. 6, (Page 268). He wrote:
“Concerning some fellows who started smoking pot — it is clearly forbidden according to several important laws of the Torah.
“1. It spoils and depletes the body.
“2. Even if the fellows are healthy and the pot won’t cause so much damage to their body, it still ruins the mind and they were be unable to understand things properly, which is even more serious. Not only [by smoking pot] are they preventing themselves from learning Torah properly, but it will also prevent them from praying and keeping the Torah commandments properly. One who does these commandments without having in mind to fulfill them, is as if he didn’t fulfill them.
“3. Even more, this person is developing in himself a craving which is far stronger than the craving to eat, which a person needs to live. Some are not able to control or overcome these cravings. This is a strict prohibition as we see concerning the rebellious son whose gluttony shows he has uncontrolled cravings for food, even though he is only eating kosher food. It goes without saying that one may absolutely not bring himself to even greater cravings and especially for a thing that a human being doesn’t need.
“4. Another reason is because the father and the mother of those who smoke dope are pained about it, and therefore, he is violating the commandment of honoring parents.
“5. He is also transgressing the positive commandment of “You shall be holy”, as the Ramban explains in Leviticus 19:2. One who smokes dope will end up transgressing many other prohibitions besides this.
“The conclusion: It is simple and straightforward that this is gravely forbidden, and one should do everything possible to eliminate this impurity from the Jewish people, and especially those who study in yeshivas.” This is the end of his responsa.
Wishing you the best,