Mono-Amine-Oxidase is an enzyme which breaks down certain poisons in our diet. It also breaks down goodies like psilocybin and DMT. An MAO Inhibitor such as Syrian Rue or the ayahuasca vine (B. Caapi) allows these drugs to become orally active.
MAOIs are also used as antidepressants. If you are on an MAOI, stay the hell away from: