What Is Mao The Enzyme Behind Mood And Movement?

Monoamine oxidase, or MAO, is an enzyme in your body that breaks down certain brain chemicals—specifically serotonin, dopamine, and norepinephrine. These chemicals, called monoamines, directly control your mood, focus, and physical movement. By clearing out these molecules after they have done their job, MAO keeps the levels balanced. When this enzyme does not work properly, or when it is blocked by medication, those brain chemical levels change, which can affect both how you feel and how you move.

What Exactly Does MAO Do in the Brain?

Think of MAO as a recycling system. After a nerve cell releases a chemical like dopamine to send a signal to the next cell, the leftover chemical needs to be cleared away. If it stays too long, the signal keeps firing. MAO steps in and breaks down these leftover molecules so the system can reset.

This process matters because the timing of brain signals is precise. Dopamine is not just about pleasure—it is essential for coordinating smooth, controlled movement. Serotonin regulates mood, appetite, and sleep. Norepinephrine helps with alertness and the stress response. MAO keeps all three of these in check.

There are actually two forms of this enzyme in the human body: MAO-A and MAO-B. They do similar work but prefer different chemicals. MAO-A mainly breaks down serotonin, norepinephrine, and dopamine. MAO-B mainly breaks down dopamine and a different molecule called phenylethylamine. This distinction matters because medications can target one form without affecting the other.

Where Is MAO Found in the Body?

MAO is not only in the brain. It is present in many tissues throughout the body, including the liver, intestines, and blood platelets. In the digestive tract and liver, MAO serves as a protective barrier. It breaks down monoamines that come from food, preventing them from entering your bloodstream in large amounts.

This is why certain foods can interact dangerously with MAO inhibitor medications. Foods that are aged, fermented, or cured—like aged cheese, cured meats, and some beers—contain high levels of a monoamine called tyramine. Normally, MAO in your gut breaks down tyramine before it causes problems. But if you take an MAO inhibitor, that enzyme is blocked, and tyramine can build up to dangerous levels, causing a sudden spike in blood pressure.

In the brain, MAO is located inside the mitochondria of nerve cells. Mitochondria are the energy-producing parts of cells, and they are where MAO does its cleanup work.

What Happens When MAO Levels Are Too High or Too Low?

Some research suggests that MAO activity increases with age. Higher MAO activity means more rapid breakdown of dopamine, serotonin, and norepinephrine. Over time, this could contribute to lower levels of these important chemicals. This is one reason why some age-related conditions involve changes in mood and movement.

When MAO activity is too high, the brain may run low on dopamine and serotonin. Low dopamine is strongly linked to movement disorders. Low serotonin is linked to depression and anxiety. This is the basic logic behind why researchers have studied MAO in connection with both mood disorders and neurological conditions.

On the other hand, when MAO is blocked by medication, the levels of these monoamines rise. This is the intended effect of a class of antidepressants called monoamine oxidase inhibitors (MAOIs). They were among the first antidepressants developed, and they are still used today, though less often than newer drugs.

What Is the Link Between MAO and Movement Disorders?

The connection between MAO and movement is primarily through dopamine. Dopamine is the main chemical that controls smooth, voluntary movement. In Parkinson’s disease, the brain cells that produce dopamine gradually die off. Without enough dopamine, movement becomes stiff, slow, and shaky.

MAO-B is the form of the enzyme that breaks down dopamine in the brain. Blocking MAO-B can slow the breakdown of whatever dopamine is still being produced. This is why MAO-B inhibitors are used as a treatment for Parkinson’s disease. They do not stop the disease from progressing, but they can help manage movement symptoms by preserving dopamine levels for longer.

It is important to understand that MAO inhibitors treat symptoms—they do not cure the underlying condition. In Parkinson’s disease, the loss of dopamine-producing cells continues regardless of MAO activity. The medication simply makes better use of the dopamine that remains.

What Are MAO Inhibitors and How Are They Used?

MAO inhibitors are medications that block the action of this enzyme. They come in two main types. Nonselective MAOIs block both MAO-A and MAO-B. Selective MAOIs block only one form.

Selective MAO-B inhibitors, like selegiline and rasagiline, are used for Parkinson’s disease. They help with motor symptoms by reducing dopamine breakdown. Some research also explores whether they might slow disease progression, but the evidence for that is not conclusive.

MAO-A inhibitors and nonselective MAOIs are used for treatment-resistant depression. They can be highly effective, but they come with significant dietary restrictions. Anyone taking these medications must avoid foods high in tyramine to prevent dangerous blood pressure spikes. This dietary burden is a major reason why doctors often try other antidepressants first.

There is also a selegiline patch that delivers the drug through the skin. At lower doses, the patch may avoid some of the dietary restrictions because it bypasses the digestive system. However, dietary precautions may still be necessary at higher doses.

Can Diet or Lifestyle Change MAO Activity?

Some natural compounds have been studied for their effect on MAO activity. Green tea contains catechins that may mildly inhibit MAO in laboratory studies. Some herbal supplements are marketed for mood support based on similar ideas. The evidence for meaningful effects in humans is limited, and no herbal product has been proven to work as well as prescription MAO inhibitors.

Smoking tobacco actually inhibits MAO-A and MAO-B in the brain. This is one reason why quitting smoking can temporarily affect mood. The effect is real and measurable, but it is hardly a reason to smoke—the health risks of tobacco far outweigh any mood-related effect.

Regular exercise and adequate sleep are consistently linked to healthy dopamine and serotonin function, but they do not work by directly blocking MAO. Their effects on brain chemistry are broader and less specific.

What Is the Evidence for MAO’s Role in Depression?

MAO inhibitors are proven to be effective antidepressants. They have been studied in clinical trials for decades. However, the exact role of MAO in causing depression is not fully understood. The older theory was simple: depression was caused by low monoamines, and MAO inhibitors fixed that by preventing breakdown. The reality is more complex.

Modern research shows that depression involves multiple brain systems, inflammation, and changes in brain structure. Raising monoamine levels helps many people, but not everyone. It can take weeks for MAO inhibitors to improve mood, even though the enzyme is blocked within hours. This delay suggests that the antidepressant effect involves gradual adaptations in the brain, not just an immediate chemical shift.

Some studies suggest that MAO activity is higher in certain brain regions of people with depression. Other studies have not found this difference. The evidence is mixed, and the relationship between MAO and depression is likely different from person to person.

Are There Genetic Differences in MAO?

Yes. The genes that code for MAO-A and MAO-B have natural variations. Some of these variations affect how much enzyme your body produces or how active it is. The MAO-A gene has been studied extensively because it is located on the X chromosome.

Certain variations of the MAO-A gene have been linked in some studies to aggressive behavior and impulsivity. However, these genetic variations do not determine behavior on their own. Environmental factors and life experiences interact with genetics in complex ways. Having a particular MAO-A variant does not mean a person will develop any specific condition.