What defines antagonists in drug action?

Antagonists in drug action are characterized by their ability to bind to receptors without triggering a response or stimulation. This means that while antagonists fit into the receptor sites, they do not activate the receptors, thereby blocking or inhibiting the action of other substances, such as agonists, that would normally bind and produce a physiological response. This binding action can effectively prevent the natural ligand (a substance that normally binds to the receptor) or any agonist from activating the receptor, which can be useful in various therapeutic contexts, such as reversing the effects of opioids or managing conditions like anxiety and hypertension.

The other options do not accurately describe the function of antagonists; they either imply stimulation or enhancement of receptor activity or suggest a different mechanism of action that does not align with the fundamental definition of antagonism in pharmacology.