**Core Concept**
Clozapine is an atypical antipsychotic medication primarily used for treating treatment-resistant schizophrenia. Its pharmacological profile is characterized by a unique combination of serotonin-dopamine antagonist activity and a relatively low affinity for dopamine D2 receptors, which contributes to its distinct side effect profile.

**Why the Correct Answer is Right**
Sialorrhea, or excessive salivation, is a notable adverse effect of clozapine. This side effect is thought to be related to the medication's anticholinergic properties and its ability to inhibit the reuptake of acetylcholine. As a result, increased acetylcholine levels can stimulate salivation. In addition, clozapine's serotonin-dopamine antagonist activity may also contribute to the development of sialorrhea by affecting the balance of neurotransmitters involved in salivation regulation.

**Why Each Wrong Option is Incorrect**
**Option A:** Hypertension is not a characteristic adverse effect of clozapine, which is more commonly associated with orthostatic hypotension due to its antihypertensive properties.
**Option C:** Extrapyramidal side effects (EPS) are actually less common with clozapine compared to typical antipsychotics, due to its lower affinity for dopamine D2 receptors. However, EPS can still occur, especially at higher doses.
**Option D:** Neuroleptic malignant syndrome (NMS) is a rare but life-threatening side effect of antipsychotic medications, including clozapine. However, it is not as closely associated with clozapine as sialorrhea.

**Clinical Pearl / High-Yield Fact**
When prescribing clozapine, it's essential to monitor patients for sialorrhea and other anticholinergic side effects, such as dry mouth, constipation, and urinary retention. To mitigate these effects, patients may be prescribed anticholinergic medications or other adjunctive treatments.

**✓ Correct Answer: B. Sialorrhea**