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MAOIs

High-yield Verified · Jul 2026

Prototype: phenelzine

Monoamine oxidase inhibitors — reserved for treatment-resistant depression, hedged by strict food and drug rules.

How it works in the body

The system involved, what goes wrong, and how the drug and body interact.

01 Blocking the enzyme that clears monoamines

Serotonin, norepinephrine, and dopamine are collectively called monoamines, and the enzyme monoamine oxidase (MAO) breaks them down. MAOIs block that enzyme, so all three monoamines accumulate — a broad antidepressant effect that works even in treatment-resistant and atypical depression. That efficacy is real, but the same broad action makes MAOIs the most interaction-prone antidepressants, so they are used late and carefully.

MAOIs block the enzyme that degrades monoamines — raising serotonin, norepinephrine, and dopamine.

02 The tyramine hypertensive crisis — the "wine and cheese" rule

Tyramine is an amino-acid byproduct in aged, fermented, and cured foods — aged cheese, cured/smoked meats, red wine, tap beer, soy sauce, sauerkraut, fava beans. Normally the gut’s MAO destroys tyramine before it reaches the circulation. But when MAO is blocked by an MAOI, dietary tyramine floods in and triggers a massive norepinephrine release, causing a sudden, potentially fatal hypertensive crisis (severe headache, sweating, chest pain, stroke).

Patients must follow a strict low-tyramine diet. Combining MAOIs with other serotonergic drugs (SSRIs/SNRIs, triptans, meperidine, dextromethorphan) risks lethal serotonin syndrome — which is why switching to/from an MAOI requires a 2-week washout (5 weeks after fluoxetine, which lingers).

With MAO blocked, dietary tyramine escapes breakdown → norepinephrine surge → hypertensive crisis.

Drug names

Generic Brand
phenelzine Nardil
tranylcypromine Parnate
selegiline (transdermal) Emsam

Indications

  • Treatment-resistant major depression
  • Atypical depression; some anxiety disorders
  • Selegiline (oral, higher dose) — Parkinson disease (MAO-B); transdermal for depression

Mechanism of action

Inhibit monoamine oxidase (MAO-A and/or MAO-B), preventing breakdown of serotonin, norepinephrine, and dopamine — increasing their availability. Non-selective irreversible inhibitors (phenelzine, tranylcypromine) also block gut MAO, creating the tyramine interaction.

In plain terms
They stop the enzyme that clears the brain’s mood chemicals, so more of them stick around — but they also let food-borne tyramine cause dangerous blood-pressure spikes.

Therapeutic effects — what you'll see working

Effective for hard-to-treat depression, but only if the patient can reliably follow the diet and drug restrictions. Mood benefit takes weeks; the safety teaching is the centerpiece.

Antidepressant effect
Antidepressant effect
Raising all three monoamines relieves depression, including atypical and treatment-resistant forms that fail other agents.

Adverse effects

Beyond ordinary effects (orthostasis, insomnia, weight change), the two life-threatening events — tyramine hypertensive crisis and serotonin syndrome — dominate the class.

Caution: Common
Orthostatic hypotension, insomnia/activation, weight gain, sexual dysfunction, dizziness.
Orthostatic hypotension is common day-to-day — paradoxical alongside the hypertensive-crisis risk from tyramine.
Warning: Serious Report immediately
Tyramine hypertensive crisis (aged/fermented foods); serotonin syndrome (with serotonergic drugs); many drug interactions.
A hypertensive crisis presents with sudden severe headache, palpitations, and chest pain — a medical emergency. Serotonin syndrome can be fatal; the required washouts (2 weeks, 5 for fluoxetine) exist to prevent it.
Black-box warning — most severe: ■ Boxed warning · suicidality
Increased suicidal thinking/behavior in patients < 25 early in treatment.
The antidepressant class warning applies.

Interactions

Tyramine-rich foods — aged cheese, cured/smoked meats, red wine, tap beer, fermented foods (sauerkraut, soy sauce), fava beans food
Blocked gut MAO lets tyramine trigger a norepinephrine surge → hypertensive crisis (sudden severe headache, chest pain, stroke risk).
Serotonergic drugs — SSRIs/SNRIs, triptans, meperidine, dextromethorphan, tramadol drug
Additive serotonin → potentially fatal serotonin syndrome; requires a ~2-week washout (5 weeks after fluoxetine).

Contraindications

The contraindications are all the serotonergic and sympathomimetic combinations plus the tyramine-diet requirement.

Concurrent SSRIs/SNRIs, triptans, meperidine, dextromethorphan, tramadol, other MAOIs
Risk of fatal serotonin syndrome — observe the 2-week (5-week for fluoxetine) washout.
Sympathomimetics / decongestants (pseudoephedrine), stimulants
Additive norepinephrine effects can precipitate a hypertensive crisis.
High-tyramine foods; pheochromocytoma
Tyramine (or catecholamine excess) triggers hypertensive crisis.

When to hold

Assess before giving — these findings mean hold the dose and act.

Sudden severe headache, palpitations, chest pain, or sharp BP rise — hypertensive crisis
Hold the drug and notify/treat immediately — a medical emergency.

Nursing considerations

The RN-specific layer — each action paired with the reason it matters.

Diet & interaction safety
Teach the low-tyramine diet thoroughly (avoid aged cheese, cured/smoked meats, red wine, tap beer, soy sauce, sauerkraut, fava beans).
Why: Dietary tyramine is the trigger for a potentially fatal hypertensive crisis.
Enforce washout periods (2 weeks; 5 weeks after fluoxetine) when switching antidepressants; screen every new drug/OTC.
Why: Overlap with serotonergic or sympathomimetic drugs causes serotonin syndrome or hypertensive crisis.
Patient teaching
Report sudden severe headache, palpitations, chest pain, or neck stiffness immediately.
Why: These are the warning signs of a hypertensive crisis.

Sources

Educational summary for nursing students. Always verify against current prescribing information and your institution's protocols before administering. Not medical advice.