**Question:** Drug most useful in treatment of obsessive compulsive disorder is:

A. Fluoxetine
B. Clomipramine
C. Aripiprazole
D. Olanzapine

**Core Concept:**
Obsessive-compulsive disorder (OCD) is a psychiatric disorder characterized by intrusive thoughts (obsessions) and repetitive behaviors or mental acts (compulsions) that an individual feels driven to perform due to an underlying anxiety. OCD significantly impacts daily functioning and quality of life.

**Why the Correct Answer is Right:**
Fluoxetine (Prozac) is a selective serotonin reuptake inhibitor (SSRI) that primarily increases serotonin levels in the brain. In OCD patients, a decrease in serotonin levels is believed to contribute to the development and persistence of obsessive and compulsive symptoms. By restoring the balance of serotonin, SSRIs like Fluoxetine can help alleviate these symptoms and improve the patient's overall functioning.

**Why Each Wrong Option is Incorrect:**

B. Clomipramine (Anafranil) is also an SSRI like Fluoxetine, but it is an older drug with more side effects and a higher potential for drug interactions. Thus, it may not be the first-choice treatment for OCD patients.

C. Aripiprazole (Abilify) is an atypical antipsychotic medication primarily used in the treatment of schizophrenia and bipolar disorder. Its efficacy in OCD is limited and often comes with more severe side effects compared to Fluoxetine.

D. Olanzapine (Zyprexa) is another atypical antipsychotic medication used in the treatment of psychotic disorders like schizophrenia and bipolar disorder. Similar to Aripiprazole, its use in OCD is limited and may have more severe side effects than Fluoxetine.

**Clinical Pearl:**
SSRIs, like Fluoxetine, are considered first-line treatments for OCD due to their better safety profile, efficacy, and fewer side effects compared to other options mentioned. When treating OCD, the choice of medication should be based on the patient's specific needs, comorbidities, and potential drug interactions.