Many religions have beliefs about drug use; these vary greatly, with some traditions placing the ritual use of entheogens at the center of religious activity, while others prohibit drug use altogether.

Many Ancient Greek mystery religions are hypothesized to have centered around the use of entheogen, such as the Kykeon central to the Eleusinian Mysteries. Recent research suggests that the prophesies of the Delphic Oracle were uttered by Priestesses under the influence of gaseous vapors.