MAOIs, or monoamine oxidase inhibitors, are used to treat depression. As MAOIs are powerful antidepressants, they are typically prescribed by physicians after other treatments have been attempted. In the body, MAOIs work by blocking the activity of an enzyme that breaks down monoamine neurotransmitters, such as serotonin, norepinephrine, dopamine and melatonin. Thus, taking MAOIs increases the availability of these neurotransmitters, which alleviates symptoms of depression.
Unfortunately, use of MAOIs also leads to the build-up of other molecules that can be harmful at high levels. Specifically, tyramine (which is usually broken down by monoamine oxidase) can reach toxic levels in individuals on MAOIs. Monitoring diet for tyramine intake is the best way to avoid potential complications.
Tyramine
Tyramine is a metabolite of tyrosine, one of the 20 primary amino acids. The primary role of tyramine is blood pressure regulation. Under normal circumstances, the body is able to adequately control tyramine levels by breaking down the excess amino acids. However, in individuals on MAOIs, tyramine is not further metabolized, and thus builds up in the blood and competes with other neurotransmitters. As a result of interactions with other neurotransmitters, tyramine can increase blood pressure and may lead to a stroke. A 6-8 mg increase in tyramine intake can result in symptoms of nausea and/or quickened heart rate.
Aged Cheeses
Aged cheeses like cheddar and Swiss contain high amounts of tyramine and are most likely to be the hardest dietary change for those on MAOIs. Overconsuming aged cheeses is so common that the resulting symptoms have been termed the "cheese effect." One ounce of cheese (about the size of one die) contains about 40 mg of tyramine. The fermentation and processing of aged cheeses are likely causes of the increased level of tyramine. Cottage and ricotta cheeses, which contain little tyramine, are safe for consumption.
Alcohol
Tap beer and ale are known to have high levels of tyramine (38 mg per 12 oz.), and thus should not be consumed by individuals on MAOIs. Chianti wine is also recognized as having high levels of tyramine. Bottled beer and wine (other than Chianti) are suitable alternatives, but in moderation.
Processed Meats
Dried, smoked and pickled meats, primarily due to aging and preservation additives, are high in tyramine and should be avoided. This category includes salami, dry sausage, chicken liver and pickled fish (lox, caviar). The actual tyramine content varies greatly, but can be up to 86 mg per serving.
Condiments
Many condiments are high in tyramine, but are often overlooked as sources of the amino acid because they are in mixed foods. For example, soy sauce and fish sauce are almost unavoidable when eating Asian cuisine, but should be avoided as they are high in tyramine (one teaspoon of soy sauce contains 4.7 mg of tyramine). Individuals on MAOIs should be cautious when eating foods with these condiments.
In General
Tyramine content is high in foods that are aged, processed or fermented. This includes overripe fruit. As a general rule, eating fresh foods prepared with your own ingredients is a safe way to avoid excess tyramine intake.
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