As a plant marijuana is kosher with some caveats.

If grown in Israel, its growers would have to adhere to the custom of shnat shmita (meaning, allowing the land to rest every seventh year). For American-grown marijuana, shmita does not apply; nevertheless, kosher approval may be required.

According to Chabad, “if we would know that the product in question contains just leaves and that there was no unkosher residue on the processing equipment, it would not need certification, like plain unflavored tea. On the other hand, if it would be processed and contain other additives, as appears to be the case, kosher certification would be necessary.” This only applies, however, if marijuana is ingested rather than smoked or injected.

In 1973, Rabbi Moshe Feinstein ruled the use of hashish is forbidden because it could have a deleterious effect on health and Jews are obligated to maintain their physical and mental health. He also opposed it at that time because it was illegal and that “drug dependents often turn to stealing and other nefarious means of feeding their habit.” Another reason Feinstein gave was that taking drugs against their parents’ wishes violated the command to honor our parents. One more reason was that it contradicts the Torah’s instruction not to indulge excessively in bodily pleasures.

Another rabbi, Rabbi Efraim Zalmanovich said in 2013 that “taking drugs to escape the world” is “certainly forbidden.”

Marijuana is illegal for recreational use under Israeli law but it has been legal when prescribed for medicinal purposes since the 1990s. Rabbi Menachem Genack, the CEO of OU Kosher, said that Judaism prioritizes health and therefore, “Using medical cannabis products recommended by a physician should not be regarded as a chet, a sinful act, but rather as a mitzvah, an imperative, a commandment.”

Rabbi Moshe Elefant, the chief operating officer of the Orthodox Union, told Haaretz that in life or death situations, “Jewish law clearly sets aside the kosher status of a medicine, but in other cases, it is preferable and sometimes recommended that a medicine be certified kosher.”

One interpretation is that cannabis falls under the category of kitniyot on Passover, which Ashkenazi Jews are prohibited from consuming. In 2016, Rabbi Chaim Kanievsky ruled, however, that consuming marijuana for medical reasons is also kosher for Passover.

According to Dr. Yosef Glassman, cannabis was used to make clothing, tallit and tzitzit and the roof of a Sukkah. He also found that cannabis may have been used as an anesthetic during childbirth in ancient Israel.

Glassman says that Jerusalem-based professors Raphael Mechoulam and Yechiel Gaoni isolated the active ingredient of hashish and its psychoactive component, tetrahydrocannabinol, as well as the natural human analog to THC, anandamide in the 1960s. Israeli scientists subsequently developed a strain of marijuana without THC. The Israeli government, he adds, funds research on medical marijuana.

In May 2020, Israel gave final approval for the export of medical cannabis — an industry it expects to generate hundreds of millions of dollars in revenue.

Sources: “Is Marijuana Kosher?” Chabad.org;
Susie Davidson, “Doctor Cannabis,” Forward, (December 7, 2013);
Ruth Schuster, “Marijuana Is Always Kosher, as Long as You Smoke It,” Haaretz, (January 7, 2016);
Elsa Vulliamy, “Marijuana is kosher for Passover, leading rabbi rules,” Independent, (April 22, 2016);
Aaron Philmus, “Kosher Kannabis? Judaism and Marijuana,” Sefaria;
“Medical Marijuana: It's Kosher,” NPR, (April 24, 2016);
Marcy Oster, “Israel gives final OK for export of medical cannabis,” JTA, (May 14, 2020).