**Core Concept**
Dextromethorphan is a centrally acting antitussive agent, which means it acts on the central nervous system to suppress coughing. It is a synthetic molecule derived from dextromethorphan, a compound found in the plant Duboisia hopwoodii.

**Why the Correct Answer is Right**
Dextromethorphan exerts its antitussive effects by inhibiting the release of substance P, a neurotransmitter involved in the transmission of pain and cough signals from the lungs to the brain. It also has a mild anticholinergic effect, which helps to reduce the activity of the cough center in the medulla oblongata. By binding to sigma-1 receptors in the brain, dextromethorphan produces its therapeutic effects without significantly affecting respiration or other vital functions.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because dextromethorphan is not an opioid receptor agonist like morphine or codeine.
**Option B:** Incorrect because dextromethorphan is not primarily a decongestant like pseudoephedrine or phenylephrine.
**Option C:** Incorrect because dextromethorphan is not a bronchodilator like albuterol or ipratropium.

**Clinical Pearl / High-Yield Fact**
Dextromethorphan can have a unique side effect known as the "dextromethorphan syndrome," characterized by hallucinations, euphoria, and altered perception. This is due to its action on sigma-1 receptors and can occur at therapeutic doses, especially in individuals with a history of substance abuse.

**Correct Answer:** C. Centrally acting antitussive agent