A patient of schizophrenia was started on a new drug, three months later she complains of weight gain. What is the most likely dug?
**Core Concept**
The question tests the understanding of **antipsychotic-induced side effects**, specifically **weight gain**, which is a common issue with certain **atypical antipsychotics**. This side effect is primarily due to the **histamine H1 receptor antagonism** and **serotonin 5-HT2C receptor antagonism** properties of these drugs.
**Why the Correct Answer is Right**
The most likely drug causing weight gain in a patient with schizophrenia is an **atypical antipsychotic** known for its significant **histamine H1 receptor antagonism**, such as **olanzapine**. Olanzapine's antagonism of **histamine H1 receptors** and **serotonin 5-HT2C receptors** leads to increased appetite and subsequent weight gain.
**Why Each Wrong Option is Incorrect**
**Option A:** Without the specific option provided, it's challenging to give a precise reason, but typically, drugs like **haloperidol** (a typical antipsychotic) are less likely to cause significant weight gain compared to atypical antipsychotics.
**Option B:** Similarly, without the specific option, it's hard to comment, but if it were a drug like **aripiprazole**, it's known for having a lower risk of weight gain due to its partial agonist activity at the **dopamine D2 receptor**.
**Option C:** If this option were **risperidone**, while it can cause weight gain, it's generally considered to have a lower risk compared to **olanzapine**.
**Option D:** Without the specific option, if it were a drug like **ziprasidone**, it's also known for having a lower propensity for weight gain.
**Clinical Pearl / High-Yield Fact**
It's crucial to monitor patients started on **atypical antipsychotics** like **olanzapine** for **weight gain** and **metabolic syndrome** due to the significant impact on their physical health and potential for developing **type 2 diabetes** and **dyslipidemia**.
**Correct Answer:** D. Olanzapine.