Antidepressants increase risk of suicidal thinking and behavior in children, adolescents, and young adults (18-24 years of age) with major depressive disorder and other psychiatric disorders. Phenelzine not FDA approved for treatment of depression in children ≤16 years of age. May worsen psychosis in some patients or precipitate shift to mania or hypomania in bipolar disorder. Phenelzine not FDA approved for treatment of bipolar depression. Hypertensive crisis may occur with foods or supplements high in tyramine, tryptophan, phenylalanine, or tyrosine content. May cause orthostatic hypotension (use with caution in cerebrovascular disease, cardiovascular disease, hypovolemia, or concurrent medication use which may predispose to hypotension/bradycardia). Use with caution in diabetes mellitus (sensitization to effects of insulin may occur), in glaucoma, in risk of seizures, including patients with history of seizures, head trauma, brain damage, alcoholism, or concurrent therapy with medications which may lower seizure threshold, and in hyperthyroidism. Do not use with other MAOIs or antidepressants. Concurrent use with antihypertensive agents may lead to exaggeration of hypotensive effects. MAOIs effective and generally well tolerated by older patients. May increase risks associated with electroconvulsive therapy. Discontinue at least 48 hours prior to myelography. Concurrent use of sympathomimetics (including amphetamines, cocaine, dopamine, epinephrine, methylphenidate, norepinephrine, or phenylephrine) and related compounds (methyldopa, levodopa, phenylalanine, tryptophan, or tyrosine), as well as ophthalmic α~2~-adrenergic agonists (apraclonidine, brimonidine), may result in hypertensive reactions. Concurrent use of CNS depressants, cyclobenzaprine, dextromethorphan, ethanol, meperidine, bupropion, or buspirone, may result in delirium, excitation, hyperpyrexia, seizures, and coma. Use caution with local anesthetics containing sympathomimetic agents.