**Core Concept**
Valproic acid, a widely used antiepileptic medication, has several adverse effects due to its mechanism of action as a sodium channel blocker and histone deacetylase inhibitor, leading to various clinical consequences.

**Why the Correct Answer is Right**
Valproic acid's adverse effects are primarily related to its impact on mitochondrial function, leading to hepatotoxicity, particularly in children under 2 years of age. This is due to the drug's inhibition of mitochondrial beta-oxidation, resulting in the accumulation of toxic metabolites and subsequent liver damage. Additionally, valproic acid's effects on platelet aggregation and coagulation factors contribute to its hematologic side effects.

**Why Each Wrong Option is Incorrect**
**Option A:**
This option is incorrect because while valproic acid can cause weight gain, it is not its most significant or distinctive adverse effect.

**Option B:**
This option is incorrect because, although valproic acid can cause alopecia, it is not as common or clinically significant as other adverse effects like hepatotoxicity.

**Option C:**
This option is incorrect because valproic acid's effects on the central nervous system, such as sedation and tremors, are more common than its impact on the cardiovascular system.

**Clinical Pearl / High-Yield Fact**
Valproic acid's hepatotoxicity is more pronounced in children under 2 years of age, emphasizing the importance of monitoring liver function tests in this population.

**Correct Answer: B. Alopecia. Valproic acid can cause alopecia.**