Which statement about phenelzine is correct?

• A. It is a monoamine oxidase inhibitor
• B. It is a selective serotonin reuptake inhibitor
• C. It is a tricyclic antidepressant
• D. It is a benzodiazepine

Answer: (A)

Phenelzine is a monoamine oxidase inhibitor. It irreversibly inhibits MAO-A and MAO-B in the brain, preventing the breakdown of monoamines like serotonin, norepinephrine, and dopamine. This leads to increased levels of these neurotransmitters and can help relieve depressive symptoms when other treatments haven’t worked. This mechanism is different from selective serotonin reuptake inhibitors, which only block serotonin reuptake; it’s also different from tricyclic antidepressants, which mainly affect reuptake of multiple monoamines and often have distinct side effects; and it’s not a benzodiazepine, which acts on GABA-A receptors for anxiolytic effects. Because MAO inhibition raises sensitivity to tyramine, dietary restrictions are important to avoid hypertensive reactions, and there are notable drug interactions to monitor.