## Core Concept
Non-competitive antagonism is a type of receptor antagonism where the antagonist binds to a site other than the agonist binding site on the receptor, altering the receptor's function without competing with the agonist for the active site. This type of antagonism reduces the maximum effect of the agonist without affecting its affinity.

## Why the Correct Answer is Right
In non-competitive antagonism, the antagonist decreases the maximum efficacy of the agonist but does not change the agonist's affinity for the receptor (i.e., the EC50 remains the same). This is because the antagonist binds to an allosteric site on the receptor, changing its conformation and affecting its ability to produce a response.

## Why Each Wrong Option is Incorrect
* **Option A:** If an option states that non-competitive antagonism changes the affinity of the agonist for the receptor, it is incorrect because non-competitive antagonists do not compete with the agonist for the binding site and thus do not alter the agonist's affinity (EC50 remains unchanged).
* **Option B:** If an option suggests that non-competitive antagonism increases the agonist's affinity, it is incorrect because the defining characteristic of non-competitive antagonism is that it does not affect the agonist's affinity for the receptor.
* **Option C:** If an option mentions that non-competitive antagonism reduces the maximum effect of the agonist without changing its affinity, it aligns with the definition of non-competitive antagonism and is therefore not the incorrect statement we're looking for.
* **Option D:** Without specific details on what each option (A, B, C, D) states, we focus on the principle that non-competitive antagonists decrease the maximum effect of an agonist without affecting the agonist's affinity.

## Clinical Pearl / High-Yield Fact
A key point to remember is that non-competitive inhibitors can be identified in pharmacological studies by their ability to decrease the Vmax (maximum velocity) of an enzymatic reaction or the Emax (maximum effect) of a drug without affecting Km (Michaelis constant, a measure of affinity) or EC50 (the concentration of drug where the response is half of Emax).

## Correct Answer: D.