Which class of medications primarily works as a serotonin reuptake inhibitor?

The correct answer is D, as selective serotonin reuptake inhibitors (SSRIs) are specifically designed to increase serotonin levels in the brain by inhibiting its reuptake into presynaptic neurons. By blocking the serotonin transporter (SERT), SSRIs effectively allow serotonin to remain in the synaptic cleft longer, enhancing neurotransmission and improving mood. This mechanism is foundational in treating various mood disorders, particularly major depressive disorder and anxiety disorders.

SSRIs are distinguished from other classes of antidepressants, such as serotonin-norepinephrine reuptake inhibitors (SNRIs), which also work on norepinephrine in addition to serotonin. In contrast, tricyclic antidepressants (TCAs) and monoamine oxidase inhibitors (MAOIs) have broader mechanisms, affecting multiple neurotransmitters and presenting distinct side effect profiles. Therefore, the specificity of SSRIs to primarily target serotonin reuptake differentiates them from the other medication classes listed.