Antagonist Definition | Psychology

In terms of brain chemistry, an antagonist is a chemical or drug that binds to receptors to prevent an agonist from causing a reaction. One example is when an antagonist combines with a chemical to change and inactivate it (chemical antagonism). It can also reduce the effects of a chemical by binding to a receptor but not stimulating it, thus creating fewer available receptors for that chemical (pharmacological antagonism). Lastly, an antagonist might bind to a different type of receptor and produce an effect the opposite of that chemical (physiological antagonism).