The first pass effect (or first pass metabolism) is a phenomenon of drug metabolism. Drug metabolism is the metabolism of drugs, their biochemical modification or degradation, usually through specialized enzymatic systems. ...

After a drug is swallowed, it is absorbed by the digestive system and enters the portal circulation. The absorbed drug is carried through the portal vein into the liver. A drug is any substance that can be used to modify a chemical process or processes in the body, for example to treat an illness, relieve a symptom, enhance a performance or ability, or to alter states of mind. ... For the Physics term GUT, please refer to Grand unification theory The gastrointestinal or digestive tract, also referred to as the GI tract or the alimentary canal or the gut, is the system of organs within multicellular animals which takes in food, digests it to extract energy and nutrients, and... The portal vein is a major vein in the human body draining blood from the digestive system and its associated glands. ... The liver is an organ in vertebrates, including humans. ...

The liver is responsible for metabolizing many drugs. Some drugs are so extensively metabolized by the liver that only a small amount of unchanged drug may enter the systemic circulation, so the bioavailability of the drug is reduced. Santorio Santorio (1561-1636) in his steelyard balance, from Ars de statica medecina, first published 1614 Metabolism (from μεταβολισμος (metabolismos), the Greek word for change, or overthrow (Etymonline)), is the biochemical modification of chemical compounds in living organisms and cells. ... The word circulation can mean the following: The transport of blood through the circulatory system. ... In pharmacology, bioavailability is used to describe the fraction of an administered dose of medication that reaches the systemic circulation, one of the principal pharmacokinetic properties of drugs. ...

Alternative routes of administration (e.g. intravenous, intramuscular) avoid the first pass effect. In pharmacology and toxicology, a route of administration is the path by which a drug, fluid, poison or other substance is brought into contact with the body 1. ... An intravenous drip in a hospital Intravenous therapy or IV therapy is the administration of liquid substances directly into a vein. ... Intramuscular injection is an injection of a substance directly into a muscle. ...