Entheogen is a word created to be a replacement to the words psychedelic and hallucinogen by the classical studies professor Carl A. P. Ruck of Boston University. From the man himself, entheogen means "god generated within," and is used to describe any substance that alters perception of reality in such a way that is often perceived as a mystic or religious experience.

Examples of entheogens include:
-amanita muscaria, a mushroom that is hypothosized to be the SOMA of the ancient Hindu religion, and used in cultures all over the world as a way to connect to the gods.
-Ergot and its derivatives, most famously the basis for Albert Hoffman's LSD, but also known to the ancient Greeks as the Mystery of Eleusis.
-Salvia Divinorum, a member of the mint family, used by the Mazatec indians.