Simple competitive antagonists bind to the same site as agonist but elicit no biological effect of their own. The effects of simple competitive inhibition can be described intuitively: the antagonist will shift the EC50 of the agonist, but will not change the maximum response obtainable by the agonist. In other words, one can overcome the block of a fixed concentration of antagonist with more agonist. With a single concentration of antagonist, the result is a parallel shift in the agonist concentration response.
More quantitatively, we return to equilibrium conditions and where B=antagonist and Ki is the antagonist dissociation constant:
Fractional occupancy of receptors by agonist (Y)=