**Question:** Vilazadone is a

A. selective serotonin reuptake inhibitor (SSRI)
B. selective norepinephrine reuptake inhibitor (SNRI)
C. dual serotonin and norepinephrine reuptake inhibitor (SNRI)
D. selective dopamine reuptake inhibitor (SDRI)

**Correct Answer:** C. dual serotonin and norepinephrine reuptake inhibitor (SNRI)

**Core Concept:**
Vilazadone is a medication used to treat depression, a mental health disorder characterized by persistent feelings of sadness, hopelessness, and loss of interest in activities. It belongs to a class of antidepressants called dual serotonin and norepinephrine reuptake inhibitors (SNRIs).

**Why the Correct Answer is Right:**
Vilazadone is a SNRI because it inhibits the reuptake of both serotonin and norepinephrine, two neurotransmitters involved in mood regulation. By blocking their reabsorption (the process of removing excess neurotransmitters from the synaptic cleft), SNRIs increase the availability of these neurotransmitters at the synaptic cleft, enhancing their effects and potentially improving mood and alleviating symptoms of depression.

**Why Each Wrong Option is Incorrect:**
A. Selective serotonin reuptake inhibitors (SSRIs) are a different class of antidepressants that specifically target the reuptake of serotonin without affecting norepinephrine.
B. Selective norepinephrine reuptake inhibitors (SNRIs) would target the reuptake of norepinephrine without affecting serotonin. These do not include vilazadone.
D. Selective dopamine reuptake inhibitors (SRRIs) are another class of antidepressants that target dopamine reuptake without affecting serotonin or norepinephrine. Vilazadone does not belong to this class.

**Clinical Pearl:**
The distinction between SSRIs, SNRIs, and other classes of antidepressants is crucial for understanding their pharmacology, clinical effects, and potential side effects. SNRIs like vilazadone are often preferred over SSRIs and TRIs (tricyclic antidepressants) due to their less frequent side effects and fewer potential drug interactions with other medications. However, they can cause weight gain and gastrointestinal side effects due to their mechanism of action.