MAOIs, or monoamine oxidase inhibitors, are a class of antidepressant medications that work by blocking an enzyme responsible for breaking down key brain chemicals involved in mood regulation. They were among the first antidepressants ever developed and remain some of the most effective options for people whose depression hasn’t responded to newer drugs. Today, MAOIs are considered third-line treatments, meaning they’re typically tried after other antidepressants have failed, and experts widely consider them underutilized.
How MAOIs Work in the Brain
Your brain naturally produces chemicals called neurotransmitters, including serotonin, dopamine, and norepinephrine, that regulate mood, motivation, and emotional stability. An enzyme called monoamine oxidase breaks these chemicals down after they’ve done their job. In depression, the levels of these neurotransmitters can drop too low. MAOIs block the enzyme from doing its cleanup work, which allows serotonin, dopamine, and norepinephrine to build up and remain active longer.
There are actually two forms of the enzyme. MAO-A primarily breaks down serotonin and, to a lesser extent, norepinephrine. MAO-B targets other brain chemicals, including one called phenylethylamine. Dopamine and tyramine (a compound found in certain foods) are broken down by both forms. Depending on which type of enzyme a medication blocks, its effects and side effect profile can differ significantly.
Available MAOI Medications
Several MAOIs are currently available by prescription:
- Phenelzine is used for atypical depression, a subtype where people experience mood reactivity, increased appetite, and excessive sleep rather than the classic loss of appetite and insomnia.
- Tranylcypromine is prescribed for major depressive disorder.
- Isocarboxazid is used for persistent, debilitating depression that hasn’t responded to other antidepressants.
- Selegiline is available both as an oral medication (used primarily for Parkinson’s disease) and as a skin patch marketed under the brand name EMSAM for depression.
Phenelzine, tranylcypromine, and isocarboxazid are all taken orally and block both MAO-A and MAO-B. These are the “classic” MAOIs that come with the dietary restrictions most people have heard about. The selegiline patch works differently because it delivers the drug through the skin, bypassing the digestive system. At its lowest dose (6 mg per 24 hours), the patch does not require any dietary changes at all, making it a more convenient option for many people.
Who MAOIs Are Prescribed For
MAOIs are most often considered after someone has tried and not responded to SSRIs, SNRIs, or other newer antidepressants. For people with treatment-resistant depression, they can be transformative. Researchers have described them as potentially lifesaving for severely affected individuals who have experienced multiple treatment failures. They’re also recognized as particularly effective for atypical depression, where symptoms differ from the “classic” presentation.
Despite their effectiveness, MAOIs are prescribed far less often than other antidepressants. This is largely because of the dietary restrictions and drug interactions they require, which many prescribers and patients find burdensome. Under consistent medical supervision, though, MAOIs are considered safe, effective, and low-cost.
The Tyramine Problem
The most distinctive aspect of taking an MAOI is the need to avoid foods high in tyramine, an amino acid found naturally in many aged, fermented, and cured foods. Normally, the monoamine oxidase enzyme in your gut breaks tyramine down before it can affect your blood pressure. When that enzyme is blocked by an MAOI, tyramine builds up in your bloodstream and can trigger a sudden, dangerous spike in blood pressure. In rare cases, this can cause a brain bleed.
The list of foods to avoid is extensive and worth memorizing if you’re taking one of these medications:
- Aged cheeses: cheddar, Swiss, Parmesan, blue cheeses like Stilton and Gorgonzola, brie, Camembert, feta, Gruyere, and Edam
- Cured and processed meats: pepperoni, salami, dry sausages, bologna, bacon, corned beef, and smoked fish
- Fermented foods: sauerkraut, kimchi, pickles, pickled fish, tofu, miso, and caviar
- Fermented sauces: soy sauce, fish sauce, shrimp sauce, Worcestershire sauce, and teriyaki sauce
- Fermented drinks: kombucha, kefir, and especially tap or home-brewed beer and wine
- Certain produce: fava beans, snow peas, dried fruits, overripe bananas, and overripe avocados
- Yeast-based spreads: Marmite, Vegemite, and brewer’s yeast
- Improperly stored or spoiled food
Fresh meats, fresh cheeses, and most fruits and vegetables are fine. The key pattern is that tyramine levels increase as foods age, ferment, or sit out. Leftovers that have been properly refrigerated and eaten within a day or two are generally not a concern, but food safety habits matter more on an MAOI than they do for most people.
Common Side Effects
Beyond the dietary restrictions, MAOIs share a set of everyday side effects similar to many antidepressants. These include dizziness or lightheadedness from low blood pressure, dry mouth, nausea, diarrhea or constipation, drowsiness, and insomnia. Most of these are manageable and often improve over the first few weeks as your body adjusts.
The more serious concern is a hypertensive crisis, the sudden blood pressure spike triggered by tyramine or certain drug interactions. Warning signs include a severe headache (often at the back of the head), a pounding heartbeat, neck stiffness, nausea, and sweating. This is a medical emergency and the reason the dietary guidelines exist.
Drug Interactions to Know About
MAOIs interact dangerously with a wide range of other medications. Combining an MAOI with an SSRI, SNRI, or certain pain medications can cause serotonin syndrome, a condition where serotonin levels become dangerously high. Symptoms range from agitation and rapid heart rate to muscle rigidity, seizures, and in severe cases, death.
This isn’t limited to prescription drugs. Over-the-counter cold medications containing certain decongestants can also trigger a hypertensive crisis. Cough suppressants found in many common cold remedies can raise serotonin to dangerous levels. Even some herbal supplements pose risks. If you’re on an MAOI, checking with a pharmacist before taking anything new, including seemingly harmless over-the-counter products, is essential.
Switching To or From an MAOI
One of the most important practical realities of MAOI treatment is the waiting period required when switching medications. If you’re stopping an MAOI to start a different antidepressant, or vice versa, you typically need a 14-day washout period where you take neither drug. This gives the MAOI enough time to fully clear your system so it won’t interact with the new medication.
The 14-day gap applies when switching from an MAOI to an SSRI, SNRI, or most other antidepressant classes. For two specific older antidepressants (clomipramine and imipramine), the recommended gap is even longer at 21 days. Switching between two different MAOIs also requires 14 days off medication. These waiting periods can be difficult for people with severe depression, which is one reason transitions need careful planning.
The Selegiline Patch: A Modern Option
The selegiline transdermal patch (EMSAM) represents an effort to preserve the antidepressant benefits of MAOIs while reducing the lifestyle burden. Because the medication absorbs through the skin and reaches the brain without first passing through the gut, it doesn’t block the intestinal MAO enzyme that normally handles tyramine from food. At the lowest dose of 6 mg per 24 hours, the FDA determined that no dietary modifications are necessary. Higher doses of the patch still require tyramine restrictions, but the lowest dose offers a way to access MAOI-level treatment without overhauling your diet.
For people who have cycled through multiple antidepressants without adequate relief, the patch can be a practical entry point into MAOI therapy, especially if the idea of strict dietary rules has been a barrier.