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Pharmacology
Antagonist
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Antagonist - A substance that binds a receptor but does not activate it - blocking the normal signal. The opposite of an agonist.
Also called receptor antagonistblockerantagonists
An antagonist is basically a blocker: it prevents a specific reaction in the body. To do this, it binds to a receptor (a kind of docking site on cells) but does not activate it. By occupying the spot it stops the body's own messenger from acting there - the signal is dampened or blocked.
A picture
A key that fits the lock but does not turn it - and while it sits there, the right key cannot get in. The opposite of an agonist.