MAOIs

High-yield Verified · Oct 2026

Prototype: phenelzine

MAOIs are a class of medications used for treatment-resistant major depression.

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 highly interaction-prone antidepressants, so they are used late and carefully.

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

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

Tyramine is a dietary amine — made from the amino acid tyrosine — found 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).

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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, low dose) — Parkinson disease (MAO-B)
Selegiline 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.

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.

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.

■ Boxed warning · suicidality

Increased suicidal thinking/behavior in patients < 25 early in treatment.

The antidepressant class warning applies: observe patients of all ages closely for clinical worsening, suicidality, or unusual changes in behavior, and advise families and caregivers to watch closely. Phenelzine (Nardil) is not approved for pediatric patients, and transdermal selegiline (Emsam) is contraindicated under age 12 because of the hypertensive-crisis risk. Tranylcypromine’s box also warns of hypertensive crisis with significant tyramine use: excessive high-tyramine foods or drinks, or certain drugs taken with it or after it is stopped, can trigger a crisis, so the box directs blood-pressure monitoring, medication-free intervals between it and interacting drugs, and teaching patients to avoid high-tyramine foods and beverages; it too is not approved for pediatric patients.

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.

Transdermal selegiline (Emsam) in children under 12

Labeled and boxed contraindication — increased risk of 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), and advise no alcohol.

Why: Dietary tyramine is the trigger for a potentially fatal hypertensive crisis. The Parnate and Emsam labels note that bottled and canned beers and wines contain little or no tyramine yet still advise against alcohol; the Nardil label lists all beer and wine, even alcohol-free versions, among the drinks to avoid.

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.

Common questions

What are MAOIs used for?

MAOIs are used for treatment-resistant major depression and atypical depression. Selegiline (oral, low dose) for Parkinson disease. Selegiline transdermal for depression.

How do MAOIs work?

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.

What are the serious side effects of MAOIs?

Watch for tyramine hypertensive crisis (aged/fermented foods); serotonin syndrome (with serotonergic drugs); many drug interactions; increased suicidal thinking/behavior in patients < 25 early in treatment.

When should a nurse hold MAOIs, and what safety checks apply?

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

Conditions treated

Depression & Suicide Risk

Patho · Mental & Behavioral Health

Last-line — reserved for depression unresponsive to other treatment because of dietary restrictions, adverse effects, and drug interactions (phenelzine’s niche: atypical depression). The tyramine pressor response (aged cheeses, cured or smoked meats, soy sauce, alcoholic beverages → hypertensive crisis) and serotonin syndrome with other serotonergic drugs demand a ≥ 14-day washout when switching to or from any other antidepressant.

Sources

Reviewed by Hae Suk Lee, RN

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