New medicines are now on the market that contain antibodies against either CGRP itself, or its receptor. They are called monoclonal antibodies (MABs) and are large molecules that do not cross the blood-brain barrier. They typically are not metabolized by the liver and have little direct impact on the metabolism of more conventional small-molecule drugs. They also tend to have relatively long half-lives in the body, but must be given parenterally (preferably by injection) due to very poor absorption from the digestive tract. They have been proved to be effective in people who experience migraine headaches, both with and without aura, and both episodic and chronic. These are the first class of preventive medications originally designed and approved for people with migraine. Monoclonal means all the antibodies are made from the same genetic material, although different MABs may derive from different sources, e.g. from hamster ovarian cells, from yeast cells or from humanized cell cultures. The antibodies are also made repeatedly to make them all identical, which results in difficult and relatively expensive production lines. Antibodies are proteins that counter or interfere with very specific parts of another protein or the site where a protein is supposed to bind to the receptor. Most commonly thought of in being used to prevent or fight off infections.