**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. This is in contrast to antagonists, which block the action of agonists without inducing a response themselves. Inverse agonists often decrease the activity of a receptor below its baseline level, which can be useful in treating conditions where excessive receptor activity is a problem.

**Why the Correct Answer is Right**
Inverse agonists work by binding to the same receptor as an agonist and inducing a conformational change that reduces the receptor's activity. This can be due to the inverse agonist stabilizing an inactive conformation of the receptor or blocking the access of agonists to the receptor. Inverse agonists can be particularly useful in treating conditions such as anxiety, where excessive GABA receptor activity is a problem. By decreasing GABA receptor activity below baseline, inverse agonists like benzodiazepine inverse agonists can produce anxiogenic effects.

**Why Each Wrong Option is Incorrect**
**Option A:** Antagonist - This is incorrect because antagonists block the action of agonists without inducing a response themselves. In contrast, inverse agonists induce a response opposite to that of agonists.
**Option B:** Partial agonist - This is incorrect because partial agonists bind to the same receptor as full agonists but induce a weaker response. Inverse agonists, on the other hand, induce a response opposite to that of full agonists.
**Option C:** Agonist - This is incorrect because agonists bind to a receptor and induce a response that is typically the same as the normal physiological response of the receptor. Inverse agonists induce a response opposite to that of agonists.

**Clinical Pearl / High-Yield Fact**
One key point to remember is that inverse agonists can decrease receptor activity below baseline, which can be useful in treating conditions where excessive receptor activity is a problem. This is in contrast to antagonists, which simply block the action of agonists without inducing a response themselves.

**Correct Answer: D. Inverse agonist**