**Core Concept**
Dextromethorphan and codeine are both opioid medications used as cough suppressants. However, they have distinct pharmacological profiles due to differences in their molecular structure and mechanism of action.

**Why the Correct Answer is Right**
Dextromethorphan acts as a non-selective NMDA receptor antagonist, which is responsible for its analgesic and antitussive effects. Unlike codeine, dextromethorphan does not have significant mu-opioid receptor agonist activity. This distinction in mechanism of action contributes to the differences in their efficacy and side effect profiles.

**Why Each Wrong Option is Incorrect**
**Option A:** Dextromethorphan and codeine differ in their indication for use. While both are used for cough suppression, codeine is also used for pain management. This is not the primary distinction between the two medications.
**Option B:** Dextromethorphan has a different chemical structure than codeine. However, the difference in chemical structure is not the primary reason for their distinct pharmacological properties.
**Option C:** Dextromethorphan is a more potent cough suppressant than codeine. While this may be true, it is not the primary distinction between the two medications.

**Clinical Pearl / High-Yield Fact**
Dextromethorphan can cause a range of psychoactive effects, including dissociation and euphoria, due to its action on NMDA receptors. This is a unique characteristic of dextromethorphan compared to other opioid medications like codeine.

**Correct Answer: B. Dextromethorphan and codeine differ in their chemical structure.**