What is the role of an antagonist in pharmacology?

The role of an antagonist in pharmacology is accurately described as a substance that binds to a receptor but does not activate it. This means that antagonists prevent the binding of agonists or other substances that would normally trigger a response through that receptor. By occupying the receptor site, antagonists effectively block the physiological response that would otherwise occur, thus inhibiting the effects of agonists which are substances that do activate the receptor.

Antagonists can play a crucial role in therapeutic contexts by counteracting or modulating the effects of drugs that act as agonists. For example, in cases where excessive stimulation of a receptor could lead to harmful effects, an antagonist can be used to mitigate those effects by preventing receptor activation.

In contrast, other options such as substances that activate a receptor, enhance the action of agonists, or alter the pharmacokinetics of another drug do not accurately describe antagonist behavior. Thus, option B is the most appropriate and correct characterization of an antagonist's role in pharmacology.