What is the primary action of phenelzine, an MAOI antidepressant?

Phenelzine is classified as a monoamine oxidase inhibitor (MAOI), and its primary action is to inhibit monoamine oxidase. This enzyme is responsible for breaking down neurotransmitters such as serotonin, norepinephrine, and dopamine in the brain. By inhibiting monoamine oxidase, phenelzine prevents the degradation of these neurotransmitters, leading to increased levels of serotonin, norepinephrine, and dopamine in the synaptic cleft. This mechanism is beneficial in treating depression and anxiety disorders, as it enhances mood and emotional well-being through enhanced neurotransmitter availability.

The other options do not accurately describe the main action of phenelzine. It does not block serotonin receptors, increase norepinephrine reuptake, or stimulate dopamine production directly; instead, it focuses on inhibiting the enzyme that degrades key neurotransmitters, thus increasing their overall levels and availability in the brain.