An MAOI (monoamine oxidase inhibitor) is a type of antidepressant that works by blocking an enzyme in your brain responsible for breaking down three key mood-regulating chemicals: serotonin, norepinephrine, and dopamine. By stopping this enzyme from doing its job, MAOIs allow these chemicals to build up to higher levels, which can ease depression. They were among the first antidepressants ever developed and remain some of the most effective options for people whose depression hasn’t responded to other treatments.
The term “MAOI inhibitor” is technically redundant (the “I” already stands for inhibitor), but it’s commonly used. These medications are prescribed less often than newer antidepressants like SSRIs, largely because they require dietary restrictions and carry a higher risk of serious interactions with other drugs and certain foods.
How MAOIs Work in the Brain
Your brain naturally produces an enzyme called monoamine oxidase, which breaks down neurotransmitters (chemical messengers) after they’ve done their signaling work. In people with depression, this cleanup process can reduce serotonin, norepinephrine, and dopamine to levels that are too low. MAOIs block the enzyme, so these neurotransmitters stay active in the brain longer and in greater quantities.
There are actually two forms of this enzyme. One form (MAO-A) primarily breaks down serotonin and norepinephrine, the chemicals most directly linked to mood regulation. The other form (MAO-B) primarily breaks down dopamine, which plays a bigger role in motivation, pleasure, and movement. Most MAOIs prescribed for depression block both forms, though some medications target only one. Selective MAO-B inhibitors, for instance, are more commonly used for Parkinson’s disease than for depression, since the antidepressant effect comes mainly from blocking MAO-A.
MAOIs Currently Available
Four MAOIs are currently approved for treating depression:
- Phenelzine, typically dosed at 45 to 75 mg per day
- Tranylcypromine, typically dosed at 40 to 60 mg per day
- Isocarboxazid, typically dosed up to 60 mg per day
- Selegiline transdermal patch, a skin patch that delivers 6, 9, or 12 mg over 24 hours
The first three are oral medications that require strict dietary restrictions (more on that below). The selegiline patch is notable because at its lowest dose (6 mg/day), it does not require dietary restrictions. The patch delivers the drug directly into the bloodstream, bypassing the gut, which is where most of the problematic food interactions originate. At the higher patch doses, dietary precautions are still necessary.
The Tyramine Problem
The biggest practical concern with MAOIs is their interaction with a substance called tyramine, found naturally in many common foods. Normally, the same enzyme that MAOIs block (monoamine oxidase) also breaks down tyramine in your gut before it reaches your bloodstream. When that enzyme is disabled, tyramine floods into your system and can trigger a sudden, dangerous spike in blood pressure. This is sometimes called the “cheese effect” because aged cheeses are one of the most well-known triggers.
Foods high in tyramine tend to be aged, fermented, overripe, or spoiled. The main ones to avoid include:
- Aged cheeses like cheddar, Swiss, Parmesan, blue cheese, Gorgonzola, and feta
- Fermented or craft alcoholic drinks, especially tap beer, home-brewed beer and wine, and some red wines, sherries, and liqueurs
- Yeast-extract spreads like Marmite and Vegemite
- Fermented or pickled foods, including sauerkraut and kimchi
- Improperly stored food, leftovers, or anything past its freshness date
Freshness matters a great deal. Tyramine levels rise as food ages, so eating only fresh foods is a core principle of the diet. Commercially made sourdough bread, pasteurized bottled beer, and commercial wines are generally considered safer options in moderation. Caffeinated beverages may also contain some tyramine, so limiting those is often recommended.
Drug Interactions and Serotonin Syndrome
MAOIs interact dangerously with a long list of other medications. The most serious risk is serotonin syndrome, a potentially life-threatening condition caused by too much serotonin building up in the brain. This can happen when MAOIs are combined with other antidepressants (especially SSRIs and SNRIs), certain pain medications, and even some over-the-counter cough and cold medicines containing dextromethorphan.
Symptoms of serotonin syndrome include rapid heartbeat, high fever, muscle rigidity, agitation, and confusion. It can escalate quickly and requires emergency medical attention.
Because of these risks, switching between an MAOI and most other antidepressants requires a waiting period of at least 14 days after stopping the MAOI before starting the new medication. For certain older antidepressants like clomipramine or imipramine, the recommended gap is 21 days. This washout period gives the enzyme enough time to recover its normal function. Switching in the other direction (from an SSRI to an MAOI) also requires a washout, and with some longer-acting SSRIs, that wait can be five weeks or more.
Common Side Effects
Early in treatment, the most frequently reported side effects are dizziness from blood pressure drops when standing up (orthostatic hypotension), daytime sleepiness, insomnia, and nausea. These often improve as your body adjusts to the medication over the first few weeks.
Longer-term side effects can include weight gain, muscle pain, tingling sensations, involuntary muscle jerks, and sexual dysfunction. Weight gain appears to be more of an issue with phenelzine specifically. Tranylcypromine and some newer reversible MAOIs tend to be weight-neutral.
Why MAOIs Are Still Prescribed
Despite their dietary restrictions and interaction risks, MAOIs remain valuable because they can work when other antidepressants fail. In studies of people with treatment-resistant depression (those who hadn’t improved on multiple other medications), high-dose tranylcypromine produced a response rate of 70% and a remission rate of 50%. In broader reviews, 56% of MAOI treatment courses resulted in patients being rated “much better” or “very much better.”
MAOIs have also shown particular effectiveness for atypical depression, a subtype characterized by mood reactivity (your mood brightens in response to positive events), increased appetite, excessive sleeping, heavy feelings in the limbs, and sensitivity to rejection. For this specific pattern of depression, MAOIs often outperform other antidepressant classes.
The practical reality is that MAOIs require more effort from the person taking them. You need to be aware of what you eat, carry a list of medications to avoid, and communicate with every healthcare provider you see. For many people, that trade-off isn’t worth it when simpler options are available. But for those who have tried multiple antidepressants without relief, MAOIs represent a genuinely powerful alternative that too often gets overlooked.