An agent that binds with receptors and increase its action is called agonist.

2. Agonist:
• An agent which activates a receptor to produce an effect
similar to a that of the physiological signal molecule.

3. Antagonist:
• An agent which prevents the action of an agonist on a receptor or the
subsequent response, but does not have an effect of its own.

4. Partial agonist:
• An agent which activates a receptor to produce submaximal effect
but antagonizes the action of a full agonist.

5. Inverse agonist:
• An agent which activates receptors to produce an effect in the
opposite direction to that of the agonist.
Ex. beta adrenergic Blocker