**Core Concept**
Agranulocytosis is a potentially life-threatening condition characterized by a severe and prolonged decrease in the production of granulocytes (a type of white blood cell) in the bone marrow. This condition increases the risk of infections and can be a side effect of certain medications.

**Why the Correct Answer is Right**
The correct answer to this question is **Clozapine**. Clozapine is an atypical antipsychotic medication that is known to cause agranulocytosis, a potentially fatal side effect. Clozapine works by blocking dopamine receptors in the brain, but it also affects the bone marrow, leading to a decrease in granulocyte production. Regular blood monitoring is essential when prescribing clozapine to prevent and detect agranulocytosis early.

**Why Each Wrong Option is Incorrect**
* **Option A:** Lithium is a mood stabilizer that can cause nephrotoxicity, hypothyroidism, and tremors, but it is not commonly associated with agranulocytosis.
* **Option B:** Opioids can cause respiratory depression, constipation, and dependence, but they are not typically linked to agranulocytosis.
* **Option C:** SSRIs (selective serotonin reuptake inhibitors) can cause serotonin syndrome, QT interval prolongation, and gastrointestinal side effects, but they are not commonly associated with agranulocytosis.

**Clinical Pearl / High-Yield Fact**
Regular monitoring of blood counts is crucial when prescribing clozapine to prevent agranulocytosis. A complete blood count (CBC) should be performed before initiating treatment and at regular intervals during therapy.

**Correct Answer:** C. Clozapine.