**Core Concept**
Obsessive-compulsive neurosis, now referred to as obsessive-compulsive disorder (OCD), is a chronic anxiety disorder characterized by recurring, intrusive thoughts (obsessions) and repetitive behaviors (compulsions). Effective treatment typically involves pharmacotherapy, particularly with selective serotonin reuptake inhibitors (SSRIs) or tricyclic antidepressants (TCAs) that can modulate serotonin levels.

**Why the Correct Answer is Right**
Clomipramine, a tricyclic antidepressant (TCA), is the drug of choice for treating OCD. This is due to its potent serotonin reuptake inhibition properties, which help increase serotonin levels in the brain. Serotonin plays a crucial role in regulating mood, anxiety, and obsessive-compulsive behaviors. Clomipramine's efficacy in OCD is attributed to its ability to modulate the serotonin system, thereby reducing the frequency and severity of obsessions and compulsions.

**Why Each Wrong Option is Incorrect**
**Option A:** Imipramine is another TCA, but it is not as effective as clomipramine in treating OCD. While imipramine can help with depression and anxiety, it has a weaker serotonin reuptake inhibition profile compared to clomipramine.
**Option B:** CPZ (chlorpromazine) is a typical antipsychotic medication primarily used to treat schizophrenia and acute psychosis. It is not indicated for OCD and may even exacerbate symptoms due to its potential to increase dopamine levels, which can worsen obsessive-compulsive behaviors.
**Option C:** Carbamazepine is an anticonvulsant medication used to treat epilepsy and bipolar disorder. It is not a first-line treatment for OCD and may not be effective in managing obsessive-compulsive symptoms.

**Clinical Pearl / High-Yield Fact**
When treating OCD, it's essential to note that SSRIs are generally considered first-line treatment due to their favorable side-effect profile and efficacy. However, SSRIs may take several weeks to produce significant symptom improvement, whereas clomipramine can provide faster relief, making it a useful option for patients with severe OCD.

**✓ Correct Answer: D. Clomipramine**