Marijuana should be used for medicinal purposes. This is because the benefits far outweigh the perceived risks. This is especially so for cancer patients. Marijuana used medicinally helps them undergo the tortuous and painful chemotherapy session.
I do not believe illegal drugs should be legal for religious purposes. Religion and the use of banned substances are not related at all and those who the use of drugs for religious purposes should be discouraged. Also there is no perceived health benefit and religion being a spiritual entity should not justify marijuana use.