Which monoamine oxidase inhibitor is listed in the material?

• A. Phenelzine (Nardil)
• B. Phenytoin (Dilantin)
• C. Metformin
• D. Tamoxifen

Answer: (A)

Monoamine oxidase inhibitors block the enzyme monoamine oxidase, which normally breaks down key neurotransmitters such as norepinephrine, serotonin, and dopamine. By inhibiting this enzyme, these drugs raise levels of those neurotransmitters and can help treat certain depressive disorders.

The drug that fits this mechanism among the options is phenelzine. It is a classic monoamine oxidase inhibitor.

Phenytoin is an anticonvulsant that stabilizes neuronal membranes by blocking voltage-gated sodium channels, not an MAOI. Metformin is a biguanide used to treat type 2 diabetes by reducing hepatic glucose production and improving insulin sensitivity. Tamoxifen is a selective estrogen receptor modulator used in hormone-responsive breast cancer.