Monoamine oxidase inhibitors (MAOIs)

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Monoamine oxidase inhibitors (MAOIs)

Monoamine oxidase inhibitors (MAOIs) were the first type of antidepressant developed. They're effective, but have generally been replaced by antidepressants that are safer and cause fewer side effects. MAOIs generally require diet restrictions because they can cause dangerously high blood pressure when taken with certain foods. In spite of side effects, these medications are still a good option for some people. In certain cases, they relieve depression when other treatments have failed.

How MAOIs work

Antidepressants such as MAOIs ease depression by affecting chemical messengers (neurotransmitters) used to communicate between brain cells. Most antidepressants work by changing the levels of one or more of these naturally occurring brain chemicals.

The enzyme monoamine oxidase is involved in removing the neurotransmitters norepinephrine (nor-ep-ih-NEF-rin), serotonin (ser-oh-TOE-nin) and dopamine (DOE-puh-mene) from the brain. MAOIs prevent this from happening, which makes more of these brain chemicals available. This is thought to boost mood by improving brain cell communication. MAOIs also affect other neurotransmitters in the brain and digestive system, causing side effects.

Monoamine oxidase inhibitors approved to treat depression

MAOIs approved by the Food and Drug Administration to treat depression, with their generic names followed by available brand names in parentheses, include:

  • Isocarboxazid (Marplan)
  • Phenelzine (Nardil)
  • Selegiline (Emsam, Eldepryl, Zelapar)
  • Tranylcypromine (Parnate)

Selegiline is available as a skin (transdermal) patch. Using a patch may cause fewer side effects than may MAOIs taken orally. If you're using the lowest dose patch, you may not need diet restrictions.

MAOIs are sometimes used to treat conditions other than depression.

Side effects of monoamine oxidase inhibitors

Because of side effects and safety concerns, MAOIs are most often tried when other antidepressants don't work.

Side effects of MAOIs can include:

  • Daytime sleepiness
  • Dizziness or lightheadedness
  • Low blood pressure
  • Diarrhea
  • Dry mouth
  • Altered sense of taste
  • Nervousness
  • Muscle aches
  • Insomnia
  • Weight gain
  • Reduced sexual desire or difficulty reaching orgasm
  • Inability to maintain an erection (erectile dysfunction)
  • Difficulty urinating
  • Prickling or tingling sensation in the skin (paresthesia)

Safety concerns with monoamine oxidase inhibitors

There are a number of things to consider before taking an MAOI.

  • Antidepressants and pregnancy. Some antidepressants may harm your child if you take them during pregnancy or while you're breast-feeding. If you're taking an antidepressant and you're considering getting pregnant, talk to your doctor or mental health provider about the possible dangers. Don't stop taking your medication without contacting your doctor first.
  • Food and beverage interactions. MAOIs can cause dangerous interactions with certain foods and beverages. If you take MAOIs, you'll face dietary restrictions that require you to limit foods that contain high levels of tyramine, such as many cheeses, pickled foods, certain meats, beer and wine. Tyramine is an amino acid that helps regulate blood pressure. It occurs naturally in the body and in certain foods. The interaction of tyramine with MAOIs can cause dangerously high blood pressure. Your doctor can give you a complete list of dietary restrictions.
  • Drug interactions. MAOIs can also cause serious reactions when you take them with certain other medications. Examples of medications to avoid include other antidepressants, certain pain medications, certain decongestants and some herbal supplements. Make sure you understand exactly which drugs you need to avoid. Always check with your doctor or pharmacist before taking any new prescription medication, over-the-counter medication or supplement while you're taking an MAOI.
  • Serotonin syndrome. Rarely, an MAOI can cause dangerously high levels of serotonin. This is known as serotonin syndrome. It most often occurs when two medications that raise serotonin are combined. These include other antidepressants, medications for certain health conditions and the herbal supplement St. John's wort. Signs and symptoms of serotonin syndrome include confusion, rapid or irregular heartbeat, dilated pupils, fever, and unconsciousness. Seek immediate medical attention if you have any of these signs or symptoms.

Suicide risk and antidepressants

The Food and Drug Administration (FDA) requires that all antidepressants carry a warning that some children, adolescents and young adults may be at increased risk of suicide when taking antidepressants. MAOIs are generally not prescribed to children, but anyone taking an antidepressant should be watched closely for worsening depression or unusual behavior — especially in the first few weeks after starting an antidepressant. Keep in mind, antidepressants are more likely to reduce suicide risk in the long run by improving mood.

Stopping treatment with monoamine oxidase inhibitors

Talk to your doctor before you stop taking an MAOI. Stopping treatment with MAOIs has been associated with nausea, vomiting and feeling generally unwell (malaise). Rarely, discontinuation has caused an uncommon withdrawal syndrome involving vivid nightmares with agitation, detachment from reality (psychosis) and convulsions. This is called discontinuation syndrome. If you stop an MAOI suddenly, you're more likely to experience a withdrawal-type reaction. Work with your doctor to gradually decrease your dose.

Finding the right antidepressant

Each person reacts differently to a particular antidepressant and may be more susceptible to certain side effects. Because of this, one antidepressant may work better for you than another. When choosing an antidepressant, your doctor will take into account your particular symptoms, what health problems you have, what other medications you take and what has worked for you in the past. Sometimes a combination of antidepressants may be the best treatment choice.

Inherited traits play a role in how antidepressants affect you. In some cases, DNA tests such as cytochrome P450 (CYP450) tests may give clues as to whether an antidepressant is likely to ease symptoms or cause side effects. DNA testing isn't widely used yet, but is becoming more common.

It can take a long time to find the best treatment for depression. It takes several weeks or longer before an antidepressant is fully effective and for initial side effects to ease up. You may need to try several antidepressants before you find the right one, but hang in there. With patience, you and your doctor can find a medication that works well for you.

Last Updated: 2010-12-08
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