Antagonist

Last updated August 2026

A molecule that blocks a receptor rather than activating it, preventing the normal signal. The opposite of an agonist.

In practice, whether a molecule acts as an agonist or antagonist depends on the receptor in question, not on the molecule alone, so the same compound can activate one target while blocking another. Antagonists are often used experimentally to confirm that an effect actually runs through a specific receptor. Understanding this pairing helps make sense of why some peptides are described as blockers rather than activators.

Educational reference only — not medical advice. Always follow the guidance of a qualified healthcare professional.