In pharmacology, what is the term for a drug that opposes another drug by producing opposite physiological effects?

• A. Physiological antagonist
• B. Competitive antagonist
• C. Inverse agonist
• D. Noncompetitive antagonist

Answer: (A)

When two drugs counteract each other by producing opposite physiological effects in the same tissue, that is physiological antagonism (also called functional antagonism). They achieve this not by blocking the same receptor, but by acting on different receptors or signaling pathways to drive opposite responses. For example, a drug that relaxes airway smooth muscle via β2 receptors will oppose a drug that constricts it via H1 or muscarinic receptors, yielding opposite tissue effects. This distinguishes it from other forms of antagonism that rely on blocking the same receptor (competitive antagonism), reducing constitutive receptor activity (inverse agonism), or lowering maximal response through irreversible or allosteric interference (noncompetitive antagonism).