An irreversible antagonist is a type of antagonist that binds permanently to a receptor, either by forming a covalent bond to the active site, or alternatively just by binding so tightly that the rate of dissociation is effectively zero at relevant time scales.[1] This permanently deactivates the receptor and is usually followed by rapid internalisation and recycling of the non-functional receptor protein. Irreversible enzyme inhibitors that act similarly are clinically used and include drugs such as aspirin, omeprazole and monoamine oxidase inhibitors.[2]