First pass effect can be understood to be the metabolic alteration, including degradation and elimination, of any chemical substance, including drugs, taken into the gastrointestinal tract and absorbed into the hepatic system. Depending on the chemical/drug, sometimes degradation occurs in the intestines, such as with insulin, and sometimes it occurs in the liver, such as with propranolol. Though the intestinal mucosa may be much less involved in first pass effect, it does play an active role in altering substances for elimination. The alteration or degradation further implies that there is a decrease in the concentration of the chemical before it enters the systemic circulatory system. A significant amount of first-pass effect occurs in the
