When a drug binds to a receptor and prevents a biological response, how is the drug classified?

When a drug binds to a receptor and prevents a biological response, it is classified as an antagonist. Antagonists work by occupying the receptor, thereby blocking the binding of other substances (such as agonists) that would normally activate the receptor and produce a physiological effect. This competitive or non-competitive binding inhibits the receptor's activity, leading to reduced or nullified biological effects that would have occurred had an agonist been present.

Understanding how antagonists function is essential in pharmacology, as they are commonly used in therapeutic settings to inhibit overactive pathways or to counteract the effects of other medications that may be causing adverse outcomes. In contrast, an agonist would enhance or mimic the biological response, a partial agonist would activate the receptor but produce a lesser response compared to a full agonist, and a receptor modulator may adjust the receptor's activity but does not categorically block or activate it.