What does Judaism have to say about recreational drug usage? I know that Judaism prohibits putting anything harmful into the body, but what about certain drugs that do not hurt the body? Is altering one's state of consciousness ok or not ok from a Jewish standpoint?
Your question was asked of Rabbi Moshe Feinstein, zatzal, regarding marijuana. The following is a summary of his answer:
The Torah speaks about a 'Ben Sorer Umoreh' - a rebellious son. A Ben Sorer Umoreh is a youth who steals meat and wine from his father and gobbles it down. The Torah calls for the death penalty in such a case. Since he is addicted to physical pleasures, he will ultimately do anything to support his habit, even rob and kill.
The same is true of drugs, and more so. People who use drugs usually acquire a strong hunger to maintain their habit, and can develop physical and/or psychological dependence in the early stages, and actually come to rob or harm others in order to support their habit in more advanced stages of addiction.
In general, using drugs is unhealthy. But even if no harm is done to the body, drugs reduce the concentration, commitment and consistency needed to pray, fulfill mitzvot and learn Torah properly.
Parents are usually distressed by a child's drug usage, so using drugs could lead to violating the commandment to "Honor your father and mother." This reason would apply to “children” of all ages. There is no age where one becomes exempt from honoring one’s parents.
Finally, the Torah commands "Kedoshim Tihiyu" - "You shall be holy". This means that you should not seek out and indulge in excess pleasures. They divert one’s attention from what’s really important in life and cause one to shirk his social and religious responsibilities.
Based on all the above reasons Rabbi Feinstein prohibits Marijuana and urges educators and anyone who is in a position to influence and guide others to do all they can to dissuade people from using it.
Now if you ask, what about alcohol? Don't all the above reasons apply to it as well? The answer is - Yes! In the words of the Rambam, "Someone who gets drunk is a sinner." Alcohol, when used for the sole purpose of getting intoxicated, would be in the same category as drugs. As opposed to the moderate use of wine for the purpose of making Kiddush, or commemorating the miraculous redemption of the Jews on Purim or Passover, where the drinking should be done in good taste to heighten one’s spiritual sensitivity. (There is no mitzvah getting into a reckless, foolish drunken stupor.)
Another point: using drugs, even for “recreation”, brings one in contact with “professionals” - users and, unless you “grow your own”, dealers. So, as they say, "If the drugs don't getchya, the company will..."
- Iggrot Moshe, Yoreh De'ah 3:35