Monoamine Oxidase Inhibitors (MAOIs)

For most people with depression the monoamine oxidase inhibitors are the second or third choice for medication to deal with their disorder. They have the same effectiveness as the tricyclics and SSRIs but their side effects are much more dangerous. The main problem with MAOIs is their interaction with tyramine, a chemical found in different foods. If Tyramine is eaten while taking MAOIs there is an increased risk of having a hypertensive (high blood pressure) crisis.

The way Monoamine Oxidase Inhibitors work requires first a discussion on the enzyme MAO. This enzyme is found in the liver, the intestinal wall, and terminals of monoamine-containing neurons. The function of MAO in neurons is to convert monoamine neurotransmitters such as serotonin and dopamine into inactive products. MAO inactivates tyramine and other biogenic amines in the liver and intestine. They also inactivate biogenic amines that can be found in some medications.

There are two forms of MAO in the body; MAO-A and MAO-B. MOA-A works in the brain to inactivate serotonin and in the liver it inactivates tyramine and other substances. MOA-B inactivates dopamine in the brain. The current MAOIs on the market today are non-selective, meaning they inhibit both forms of MAO.

Monoamine Oxidase Inhibitors perform their antidepressant effects by inhibiting MAO-A in the brains nerve terminals. Through this action these types of antidepressants increase the amount of nor-epinephrine and serotonin available for release in the brain which intensifies nerve transmission at noradregenic and serotonergic junctions.

Much like tricyclics and SSRIs the biochemical action occurs rapidly but the relief of the depressive effects takes time. It is thought that during this time that secondary neurochemical events are taking place that are ultimately responsible for the relief from depression.

Although MAOIs are as effective as tricyclics and SSRIs they are normally reserved for patients who are not responding to the first two choices. This is because of their potentially dangerous side effects. There is one exception to this rule. Patients with atypical depression are given MAOIs as a first choice.

Monoamine Oxidase Inhibitors have several dangerous side effects that everyone who takes them needs to be aware of.

1. Central Nervous System Stimulation – Unlike the tricyclics, MAOIs directly stimulate the CNS. If too much stimulation takes place the patient can become anxious, agitated, hypomanic and even manic.

2. Orthostatic Hypotension – MAOIs reduce blood pressure when given in therapeutic doses. Anyone taking these drugs should be aware of the signs of hypotension which include dizziness and lightheadedness. If these symptoms occur it is advised that the patient lie or sit down. The effects of hypotension can also be minimized by moving slowly when standing or sitting up.

3. Hypertensive Crisis from Dietary Tyramine – MAOIs normally cause hypotensive effects but if a patient taking these medications eats a tyramine rich food a severe hypertensive event can take place. This is usually characterized by a headache, tachycardia, high blood pressure, and nausea and vomiting.

This happens because tyramine is usually metabolized by MAO in the intestines. MAOIs inhibit MAO and the tyramine is allowed to pass through the digestive system directly into the blood stream where it comes in contact with peripheral sympathetic nerves. Tyramine stimulates the release of the accumulated nor-epinephrine causing vasoconstriction and excessive stimulation of the heart resulting in a hypertensive crisis.

All people taking MAOIs should be informed by their physician what food to avoid and given a list of them. These foods include yeast extracts, most cheeses, fermented sausages and age fish or meat.

Anyone taking monoamine oxidase inhibitors should follow their doctor's orders explicitly when it comes to what kinds of food they can and can’t eat along with other prescription medication that may negatively interact with it. They should also be educated about the symptoms of hypertensive crisis and told to seek immediate medical attention should these symptoms develop.