## Core Concept
The question pertains to the side effects of various antipsychotic medications, specifically their impact on body weight. Antipsychotics can cause significant weight gain, which is a critical consideration in the management of psychiatric disorders due to its implications on metabolic health.

## Why the Correct Answer is Right
Clozapine (Option ) and Olanzapine (Option ) are well-known for causing substantial weight gain. Risperidone (Option ) also has a risk of weight gain, although perhaps slightly less than Clozapine and Olanzapine. Among these, Aripiprazole (Option ) is recognized for having a lower risk of weight gain compared to the others listed. Aripiprazole is a partial dopamine agonist, and its pharmacological profile is associated with a more favorable side effect profile regarding weight.

## Why Each Wrong Option is Incorrect
* **Option A:** Clozapine is associated with a high risk of weight gain, among other metabolic side effects.
* **Option B:** Olanzapine also causes significant weight gain and is often used as a reference for drugs with high weight gain potential.
* **Option C:** Risperidone does cause weight gain, though the extent may vary among individuals.

## Clinical Pearl / High-Yield Fact
A key point to remember is that when selecting an antipsychotic, consideration of side effects such as weight gain is crucial, especially in patients with or at risk for metabolic disorders. Aripiprazole stands out as having a lower propensity for causing weight gain compared to many other antipsychotics.

## Correct Answer: D. Aripiprazole