What is the difference between an agonist and an antagonist?

• A. An antagonist binds and blocks activation, whereas agonist binds and activates.
• B. An agonist binds and activates a receptor to produce a response.
• C. Both activate receptor.
• D. An agonist binds but blocks activation.

Answer: (B)

In pharmacology, the key difference is about what each molecule does at a receptor. An agonist binds to a receptor and activates it, producing a cellular response. An antagonist, on the other hand, binds to the same receptor but blocks activation, preventing the usual response from occurring. So the clearest statement is that an agonist binds and activates a receptor to produce a response. The idea that a blocker prevents activation is true for an antagonist, but the essential contrast is that the agonist brings about activation, whereas the antagonist prevents it.