Classifications: central nervous system agent; psychotherapeutic; antidepressant; monoamine oxidase (mao) inhibitor
Pregnancy Category: C


15 mg tablets


Potent hydrazine (monoamine oxidase) MAO inhibitor. Precise mode of action is not known. Antidepressant and diverse effects believed to be due to irreversible inhibition of MAO, thereby permitting increased concentrations of endogenous epinephrine, norepinephrine, serotonin, and dopamine within presynaptic neurons and at receptor sites. Also thought to inhibit hepatic microsomal drug-metabolizing enzymes; thus it may intensify and prolong the effects of many drugs.

Therapeutic Effects

Antidepressant utilization of the drug is limited to individuals who do not respond well to other classes of antidepressants. Termination of drug action depends on regeneration of MAO, which occurs 2–3 wk after discontinuation of therapy.


Management of endogenous depression, depressive phase of manic-depressive psychosis, and severe exogenous (reactive) depression not responsive to more commonly used therapy.


Hypersensitivity to MAO inhibitors; pheochromocytoma; hyperthyroidism; CHF, cardiovascular or cerebrovascular disease; impaired kidney function, hypernatremia; atonic colitis; glaucoma; history of frequent or severe headaches; history of liver disease, abnormal liver function tests; older adult or debilitated patients; paranoid schizophrenia. Safety during pregnancy (category C), lactation, or in children <6 y of age is not established.

Cautious Use

Epilepsy; pyloric stenosis; diabetes; depression accompanying alcoholism or drug addiction; manic-depressive states; agitated patients; suicidal tendencies; chronic brain syndromes; history of angina pectoris.

Route & Dosage

Adult: PO 15 mg t.i.d., rapidly increase to at least 60 mg/d, may need up to 90 mg/d



Adverse Effects (1%)

Body as a Whole: Dizziness or vertigo, headache, orthostatic hypotension, drowsiness or insomnia, weakness, fatigue, edema, tremors, twitching, akathisia, ataxia, hyperreflexia, faintness, hyperactivity, marked agitation, anxiety, seizures, trismus, opisthotonos, respiratory depression, coma. CNS: Mania, hypomania, confusion, memory impairment, delirium, hallucinations, euphoria, acute anxiety reaction, toxic precipitation of schizophrenia, convulsions, peripheral neuropathy. CV: Hypertensive crisis (intense occipital headache, palpitation, marked hypertension, stiff neck, nausea, vomiting, sweating, fever, photophobia, dilated pupils, bradycardia or tachycardia, constricting chest pain, intracranial bleeding), hypotension or hypertension, circulatory collapse. GI: Constipation, dry mouth, nausea, vomiting, anorexia, weight gain. Hematologic: Normocytic and normochromic anemia, leukopenia. Skin: Hyperhidrosis, skin rash, photosensitivity. Special Senses: Blurred vision.

Diagnostic Test Interference

Phenelzine may cause a slight false increase in serum bilirubin.


Drug: tricyclic antidepressants may cause hyperpyrexia, seizures; fluoxetine, sertraline, paroxetine may cause hyperthermia, diaphoresis, tremors, seizures, delirium; sympathomimetic agents (e.g., amphetamine, phenylephrine, phenylpropanolamine), guanethidine and reserpine may cause hypertensive crisis; cns depressants have additive CNS depressive effects; opiate analgesics (especially meperidine) may cause hypertensive crisis and circulatory collapse; buspirone, hypertension; general anesthetics, prolonged hypotensive and CNS depressant effects; hypertension, headache, hyperexcitability reported with dopamine, methyldopa, levodopa, tryptophan; metrizamide may increase risk of seizures; hypotensive agents and diuretics have additive hypotensive effects. Food: Aged meats or aged cheeses, protein extracts, sour cream, alcohol, anchovies, liver, sausages, overripe figs, bananas, avocados, chocolate, soy sauce, bean curd, natural yogurt, fava beans—tyramine-containing foods—may precipitate hypertensive crisis. Avoid chocolate or caffeine. Herbal: Ginseng, ephedra, ma huang, St. John's wort may cause hypertensive crisis.


Absorption: Readily absorbed from GI tract. Onset: 2 wk. Metabolism: Rapidly metabolized. Elimination: 79% of metabolites excreted in urine in 96 h.

Nursing Implications

Assessment & Drug Effects

Patient & Family Education

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug