## Core Concept
Inverse agonists are a class of drugs that bind to the same receptor as an agonist but induce a pharmacological response opposite to that of the agonist. They not only block the action of the agonist but also decrease the constitutive activity of the receptor, meaning they can reduce the receptor's activity below the baseline level seen in the absence of any drug.

## Why the Correct Answer is Right
The correct statement regarding inverse agonists is that they decrease the constitutive activity of a receptor. Constitutive activity refers to the ability of a receptor to be active even in the absence of its endogenous ligand. Inverse agonists work by reducing this baseline activity, thereby producing an effect opposite to that of agonists, which increase receptor activity. This property is particularly relevant for receptors that exhibit constitutive activity under physiological conditions.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because inverse agonists do have an effect on receptors with constitutive activity; in fact, their ability to decrease this constitutive activity is a defining characteristic.
- **Option B:** This option is incorrect because inverse agonists do bind to receptors, and their action is not limited to blocking agonist access but also involves actively reducing receptor activity.
- **Option C:** This option is incorrect because inverse agonists do produce a pharmacological effect, specifically a decrease in receptor activity, which is opposite to that of agonists.

## Clinical Pearl / High-Yield Fact
A key point to remember is that inverse agonists have the potential to be therapeutic in conditions where constitutive receptor activity contributes to disease pathology. For example, the drug gabapentin acts as an inverse agonist at certain voltage-gated calcium channels, which is beneficial in treating epilepsy and neuropathic pain.

## Correct Answer Line
**Correct Answer: D.**