Which statement correctly describes an antagonist?

A. Drugs that produce the opposite effect of an agonist: While some antagonists may block the action of agonists, they do not necessarily produce an opposite physiological effect. Their primary function is to prevent receptor activation rather than generate a counteractive response. B. Drugs that inhibit cell function by occupying receptor sites: Antagonists bind to specific receptor sites without activating them, effectively blocking agonists or endogenous ligands from producing their effects. This receptor occupancy inhibits or diminishes cellular responses, making antagonists useful for controlling overstimulation or pathological signaling pathways. C. Drugs that always speed up a physiologic process: This description applies to agonists or stimulatory drugs, not antagonists. Antagonists do not inherently accelerate processes; their role is to prevent or reduce receptor-mediated activity. D. Drugs that produce effects similar to naturally occurring hormones: Agonists mimic endogenous molecules and activate receptors to produce physiological effects. Antagonists, in contrast, block these effects rather than replicate them.