What are drugs that bind to receptor sites and inhibit their natural functions called?

Drugs that bind to receptor sites and inhibit their natural functions are known as antagonists. These substances attach to specific receptors in the body, preventing the normal endogenous (natural) molecules from activating those receptors. By blocking the receptor sites, antagonists effectively inhibit the biological responses that would typically occur when the receptor is activated.

For example, in the context of neurotransmitter receptors in the nervous system, an antagonist might block a receptor that would normally be activated by a neurotransmitter, thereby diminishing or completely stopping the physiological effect that the neurotransmitter would have induced. This action is crucial in various therapeutic scenarios, such as in the treatment of conditions like hypertension or anxiety, where you may want to inhibit certain receptor activities to achieve the desired effect.

Other terms listed do not fit this description: agonists actually activate receptors to produce a biological response, histamines are compounds involved in immune responses and can act as signaling molecules, and vasodilators are drugs that relax blood vessels to increase blood flow, typically not causing inhibition at receptor sites. Thus, the role and action of antagonists make them distinctly different from the other options provided.