 Being more direct, it is often faster, and it ensures that the substance will risk degradation only by salivary enzymes before entering the bloodstream, whereas orally administered drugs must survive passage through the hostile environment of the gastrointestinal tract, which risks degrading them, by either stomach acid or bile, or by enzymes such as monoamine oxidase (MAO).Furthermore, after absorption from the gastrointestinal tract, such drugs must pass to the liver, where they may be extensively altered; this is known as the first pass effect of drug metabolism.Due to the digestive activity of the stomach and intestines, the oral route is unsuitable for certain substances, such as salvinorin A.