What type of substance decreases the effect of a neurotransmitter by blocking its sites?

An antagonist is a type of substance that decreases the effect of a neurotransmitter by blocking its binding sites on receptors. When an antagonist binds to a receptor, it prevents the natural neurotransmitter from attaching and activating the receptor. This leads to a reduction or inhibition of the neurotransmitter's intended effects in the nervous system.

For instance, if a neurotransmitter is typically responsible for stimulating or activating a certain physiological response, the presence of an antagonist will inhibit that activation, thereby altering the overall response. Understanding the role of antagonists is crucial in fields like pharmacology and neurobiology, where they can be used in the treatment of various conditions by modulating neurotransmitter activity.