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MAOIs (phenelzine, tranylcypromine, isocarboxazid, selegiline)

Monoamine oxidase inhibitor — antidepressant

Mechanism of action

Irreversibly inhibit monoamine oxidase, the enzyme that breaks down serotonin, norepinephrine, dopamine, and tyramine. Result: more monoamines available, antidepressant effect over weeks. Used for treatment-resistant depression, atypical depression, and (selegiline) Parkinson's disease. Limited use because of dietary and drug interactions.

Adverse effects

Life-threatening / NCLEX-tested

  • Hypertensive crisis from tyramine-rich foods or sympathomimetics — life-threatening (occipital headache, palpitations, sweating, severe hypertension); managed with phentolamine
  • Serotonin syndrome with serotonergic agents (SSRIs, SNRIs, TCAs, triptans, tramadol, meperidine, dextromethorphan, St. John's wort, linezolid) — life-threatening
  • Severe orthostatic hypotension
  • Insomnia, restlessness, agitation
  • Hepatotoxicity
  • Suicidality risk in patients < 25 (boxed warning)
  • Withdrawal — anxiety, agitation, psychosis if abrupt

Side effects

Common — what to teach

  • Dry mouth
  • Constipation
  • Mild dizziness, headache
  • Drowsiness or insomnia
  • Sexual dysfunction
  • Weight gain

Food & drug interactions

ABSOLUTE: SSRIs, SNRIs, TCAs, triptans, tramadol, meperidine, dextromethorphan, linezolid (it's also an MAOI), St. John's wort, sympathomimetics (decongestants like pseudoephedrine, phenylephrine), stimulants (amphetamines, cocaine). Tyramine-rich foods (aged cheeses, cured meats, fermented soy, draft/tap beer, fava beans, sauerkraut) precipitate hypertensive crisis. Wait 14 days between MAOI and most other antidepressants (5 weeks for fluoxetine).

Nursing implications

Assessment, monitoring, patient teaching

  • Detailed dietary counseling: aged/strong cheeses (cheddar, blue, parmesan), cured meats (salami, pepperoni), pickled or fermented foods (sauerkraut, kimchi), soy sauce/miso, fava beans, draft/unpasteurized beer, aged red wine, smoked or pickled fish, overripe banana — strict avoidance throughout therapy and 2 weeks after stopping
  • OTC drug counseling: avoid pseudoephedrine, phenylephrine, dextromethorphan, weight-loss supplements, stimulants, St. John's wort — pharmacist consult before any OTC
  • Teach hypertensive crisis warning signs: SEVERE occipital headache + sweating + chest pain/palpitations + severe hypertension — call 911
  • Counsel slow position changes — orthostatic hypotension is common
  • Effect takes 2–6 weeks; do not stop abruptly
  • Reconcile every drug change with the prescriber — small lists of safe analgesics, anesthetic agents, and OTCs are essential
  • Wear medical alert ID; keep an updated card of food/drug avoidance

When to hold / contraindications

  • Hypertensive crisis or severe new headache + autonomic symptoms
  • Suspected serotonin syndrome
  • Recent SSRI/SNRI/TCA exposure within washout window
  • Imminent surgery (most anesthetics interact — coordinate well in advance)
  • Severe hepatic impairment
  • Active suicidal crisis without safety plan

Memory anchor

MAOIs = "avoid aged cheese, aged meat, aged wine, aged beer, fava beans, decongestants, dextromethorphan, and most antidepressants." 14-day washout (5 weeks for fluoxetine). Hypertensive crisis: occipital headache.

Reminder: Drug cards are study aids, not clinical guidance. Always cross-check doses, holds, and contraindications with your facility's formulary and your clinical instructors before patient care.

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