Monoamine Oxidase Inhibitors

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Monoamine Oxidase Inhibitors


Monoamine oxidase inhibitors (MAO inhibitors) are medicines that relieve certain types of mental depression.


MAO inhibitors are a type of antidepressant and are used to treat mental depression. Like other antidepressant drugs, MAO inhibitors help reduce the extreme sadness, hopelessness, and lack of interest in life that are typical in people with depression. MAO inhibitors are especially useful in treating people whose depression is combined with other problems such as anxiety, panic attacks, phobias, or the desire to sleep too much.


Discovered in the 1950s, MAO inhibitors work by correcting chemical imbalances in the brain. Normally, natural chemicals called neurotransmitters carry signals from one brain cell to another. Some neurotransmitters, such as serotonin and norepinephrine, play important roles in controlling mood. But other substances in the brain may interfere with mood control by breaking down these neurotransmitters. Researchers believe that MAO inhibitors work by blocking the chemicals that break down serotonin and norepinephrine. This gives the neurotransmitters more time to do their important work.

Because MAO inhibitors also affect other chemicals throughout the body, these drugs may produce many unwanted side effects. They can be especially dangerous when taken with certain foods, beverages and medicines. Anyone taking these drugs should ask his or her physician or pharmacist for a list of products to avoid.

MAO inhibitors are available only with a physician's prescription. They are sold in tablet form. Some commonly used MAO inhibitors are isocarboxazid (Marplan), phenelzine (Nardil), and tranylcypromine (Parnate).

Recommended dosage

The recommended dosage depends on the type of MAO inhibitor and the type of depression for which it is being taken. Dosages may be different for different patients. Check with the physician who prescribed the drug or the pharmacist who filled the prescription for the correct dosage.

Always take MAO inhibitors exactly as directed by your physician. Never take larger or more frequent doses, and do not take the drug for longer than directed. See the physician regularly while taking this medicine, especially in the first few months of treatment. The physician will check to make sure the medicine is working as it should and will note unwanted side effects. The physician may also need to adjust the dosage during this period.

Several weeks may be needed for the effects of this medicine to be felt. Be sure to keep taking it as directed, even if it does not seem to be helping.

Do not stop taking this medicine suddenly. Tapering the dose may be necessary to reduce the chance of withdrawal symptoms. If it is necessary to stop taking the drug, check with the physician who prescribed it for instructions on how to stop.

MAO inhibitors may be taken with or without food, on a full or empty stomach. Check package directions or ask the physician or pharmacist for instructions on how to take the medicine. Remember that some foods and beverages must be avoided during treatment with MAO inhibitors.


The effects of this medicine may continue for 2 weeks or more after patients stop taking it. All precautions should be observed during this period, as well as throughout treatment with MAO inhibitors.

MAO inhibitors may cause serious and possibly life-threatening reactions, such as sudden high blood pressure, when taken with certain foods, beverages, or medicines. The dangerous reactions may not begin until several hours after consuming these things. Aged cheeses, red wines, smoked or pickled meats, chocolate, caffeinated beverages, and foods containing monosodium glutamate (MSG) are among the foods and drinks to be avoided. Be sure to get a complete list from the physician who prescribed the medicine or the pharmacist who filled the prescription.

Do not drink any alcoholic beverages or reduced-alcohol or alcohol-free beer or wine while taking this medicine.

Anyone who is taking MAO inhibitors should not use any other medicine unless it has been approved or prescribed by a physician who knows that they are taking MAO inhibitors. This includes nonprescription (over-the-counter) medicines such as sleep aids; medicines for colds, cough, hay fever, or asthma (including nose drops or sprays); medicines to increase alertness or keep from falling asleep; and appetite control products.

Because MAO inhibitors work on the central nervous system, they may add to the effects of alcohol and other drugs that slow down the central nervous system, such as antihistamines, cold medicine, allergy medicine, sleep aids, medicine for seizures, tranquilizers, some pain relievers, and muscle relaxants. Anyone taking MAO inhibitors should check with his or her physician before taking any of the above.

MAO inhibitors may interact with medicines used during surgery, dental procedures, or emergency treatment. These interactions could increase the chance of side effects. Anyone who is taking MAO inhibitors should be sure to tell the health care professional in charge before having any surgical or dental procedures or receiving emergency treatment.

Some people feel drowsy, dizzy, lightheaded, or less alert when using MAO inhibitors. The drugs may also cause blurred vision. For these reasons, anyone who takes these drugs should not drive, use machines or do anything else that might be dangerous until they have found out how the drugs affect them.

These medicines also make some people feel lightheaded, dizzy, or faint when they get up after sitting or lying down. To lessen the problem, get up gradually and hold onto something for support if possible.

Older people may be especially sensitive to the effects of MAO inhibitors. This may increase the chance of side effects, such as dizziness or lightheadedness.

Special conditions

People with certain medical conditions or who are taking certain other medicines can have problems if they take MAO inhibitors. Before taking these drugs, be sure to let the physician know about any of these conditions:

ALLERGIES. Anyone who has had unusual reactions to MAO inhibitors in the past should let his or her physician know before taking the drugs again. The physician should also be told about any allergies to foods, dyes, preservatives, or other substances.

PREGNANCY. Studies suggest that taking MAO inhibitors during pregnancy may increase the risk of birth defects or problems in the newborn after birth. Women who are pregnant or who may become pregnant should check with their physicians before using MAO inhibitors.

BREASTFEEDING. MAO inhibitors may pass into breast milk, but no problems have been reported in nursing babies whose mothers took the medicine. Women who are breastfeeding their babies should check with their physicians before using this medicine.

DIABETES. MAO inhibitors may affect blood sugar levels. Persons with diabetes who are taking this medicine and notice changes in their blood or urine tests should check with their physicians.

ANGINA. MAO inhibitors may make people feel unusually energetic and healthy. People with angina (chest pain) should be careful not to overexert themselves and should check with their physicians before increasing their levels of activity or exercise.

OTHER MEDICAL CONDITIONS. Before using MAO inhibitors, people with any of these medical problems should make sure their physicians are aware of their conditions:

  • Alcohol abuse
  • High blood pressure
  • Recent heart attack or stroke
  • Heart or blood vessel disease
  • Liver disease
  • Kidney disease
  • Frequent or severe headaches
  • Epilepsy
  • Parkinson's disease
  • Current or past mental illness
  • Asthma or bronchitis
  • Overactive thyroid
  • Pheochromocytoma (a tumor of the adrenal gland).

USE OF CERTAIN MEDICINES. Taking MAO inhibitors with certain other drugs may affect the way the drugs work or may increase the chance of side effects.

Side effects

The most common side effects are dizziness, lightheadedness, drowsiness, tiredness, weakness, blurred vision, shakiness or trembling, restlessness, sleep problems or twitching during sleep, increased appetite (especially for sweets), weight gain, decreased sexual ability, decreased amount of urine, and mild headache. These problems usually go away as the body adjusts to the drug and do not require medical treatment unless they interfere with normal activities.

More serious side effects may occur. If any of the following side effects occur, stop taking the medicine and get emergency medical attention immediately:

  • Severe chest pain
  • Severe headache
  • Stiff, sore neck
  • Enlarged pupils
  • Increased sensitivity of eyes to light
  • Fast or slow heartbeat
  • Sweating, with or without fever or cold, clammy skin
  • Nausea and vomiting.

Other side effects may occur. Anyone who has unusual or troublesome symptoms after taking MAO inhibitors should get in touch with his or her physician.


MAO inhibitors may interact with many other medicines. When this happens, the effects of one or both of the drugs may change or the risk of side effects may be greater. Anyone who takes MAO inhibitors must check with his or her physician before taking any other prescription or nonprescription (over-the-counter) medicine. Among the drugs that may interact with MAO inhibitors are:

  • Central nervous system (CNS) depressants such as medicine for allergies, colds, hay fever, and asthma; sedatives; tranquilizers; prescription pain medicine; muscle relaxants; medicine for seizures; sleep aids; barbiturates; and anesthetics
  • Medicine for high blood pressure
  • Other antidepressants, including tricyclic antidepressants (such as Tofranil and Norpramin), antidepressants that raise serotonin levels (such as Prozac and Zoloft), and bupropion (Wellbutrin)
  • Diabetes medicines taken by mouth
  • Insulin
  • Water pills (diuretics).

The list above does not include every drug that may interact with MAO inhibitors. Check with a physician or pharmacist before combining MAO inhibitors with any other prescription or nonprescription (over-the-counter) medicine.


Anxiety Worry or tension in response to real or imagined stress, danger, or dreaded situations. Physical reactions, such as fast pulse, sweating, trembling, fatigue, and weakness may accompany anxiety.

Central nervous system The brain and spinal cord.

Depression A mental condition in which people feel extremely sad and lose interest in life. People with depression may also have sleep problems and loss of appetite and may have trouble concentrating and carrying out everyday activities.

Neurotransmitter A chemical that carries messages from one nerve cell to another.

Phobia An intense, abnormal, or illogical fear of something specific, such as heights or open spaces.

Withdrawal symptoms A group of physical or mental symptoms that may occur when a person suddenly stops using a drug to which he or she has become dependent.