In pharmacology, what does the term "agonist" refer to?

The term "agonist" in pharmacology refers specifically to a substance that activates a receptor, leading to a biological response. This occurs when the agonist binds to a receptor and mimics the action of a natural ligand (such as a neurotransmitter or hormone), effectively stimulating the same pathways associated with that receptor. For instance, when an agonist binds to a receptor in the brain, it can result in increased neuronal excitability, signaling, or other physiological effects depending on the receptor type involved.

In the context of pharmacology, agonists are critical for understanding drug action and therapeutic effects. They are widely used in treatments where enhancing certain biological responses is beneficial, such as in the case of medications for depression or anxiety that target neurotransmitter receptors.