What is the effect of a noncompetitive antagonist on the dose–response curve?

What is the effect of a noncompetitive antagonist on the dose–response curve?

• A. Curve shifts left with unchanged maximum.
• B. No change in curve shape.
• C. Curve becomes steeper with same maximum.
• D. Curve shifts right and downward; maximal response is reduced and cannot be fully restored.

Answer: (D)

Noncompetitive antagonism lowers how much effect the receptor can produce, because the antagonist changes receptor function in a way that the agonist cannot overcome simply by increasing its amount. That leads to a dose–response curve that both shifts to the right (more agonist needed to reach a given effect) and drops in height (the maximal achievable response is reduced). Even with very high concentrations of agonist, you can’t reach the original maximum because the receptor signaling is impaired. This pattern is distinct from competitive antagonism, which shifts the curve to the right without reducing the maximum.

Noncompetitive antagonism lowers how much effect the receptor can produce, because the antagonist changes receptor function in a way that the agonist cannot overcome simply by increasing its amount. That leads to a dose–response curve that both shifts to the right (more agonist needed to reach a given effect) and drops in height (the maximal achievable response is reduced). Even with very high concentrations of agonist, you can’t reach the original maximum because the receptor signaling is impaired. This pattern is distinct from competitive antagonism, which shifts the curve to the right without reducing the maximum.