Monoamine oxidase inhibitors (MAOIs) were the first type of antidepressant in use, dating back to the 1950s.

Researchers believe MAOIs relieve depression by preventing the enzyme monoamine oxidase from metabolizing the neurotransmitters norepinephrine (nor-ep-ih-NEF-rin), serotonin (ser-oh-TOE-nin) and dopamine (DOE-puh-mene) in the brain. As a result, these levels remain high in the brain, boosting mood.

Here are the MAOIs that have been specifically approved by the Food and Drug Administration to treat depression, with their generic or chemical names followed by available brand names in parentheses:

• Phenelzine (Nardil)
• Tranylcypromine (Parnate)
• Isocarboxazid (Marplan)
• Selegiline (Emsam)

Emsam is the first skin (transdermal) patch for depression. You apply a new Emsam patch to your torso, thigh or upper arm each day, allowing the medication to be absorbed into your bloodstream over a 24-hour period.

Some of these medications may also be used to treat conditions other than depression.

Because they can cause serious side effects, MAOIs are usually reserved for people whose depression doesn't improve with other antidepressant medications they've tried first.

Side effects of MAOIs include:

• Drowsiness
• Constipation
• Nausea
• Diarrhea
• Stomach upset
• Fatigue
• Dry mouth
• Dizziness
• Low blood pressure
• Lightheadedness, especially when getting up from a lying or sitting position
• Decreased urine output
• Decreased sexual function
• Sleep disturbances
• Muscle twitching
• Weight gain
• Blurred vision
• Headache
• Increased appetite
• Restlessness
• Shakiness
• Trembling
• Weakness
• Increased sweating

MAOIs can cause dangerous interactions with certain foods and beverages. If you take MAOIs, you'll face dietary restrictions that require you to limit consumption of foods that contain a high level of tyramine, such as many cheeses, pickled foods, chocolates, certain meats, beer, wine, and alcohol-free or reduced-alcohol beer and wine. The interaction of tyramine with MAOIs can cause a dangerously high increase in blood pressure, which can lead to a stroke. Your health care professional can give you a complete list of dietary restrictions.

Emsam may offer a way to avoid these dietary restrictions. At its lowest dose of 6 milligrams a day, you don't need to follow those dietary restrictions. At higher doses of Emsam, you do, though. Talk to your doctor or mental health professional to see if this may be an option for you.

MAOIs can also cause serious reactions when you take them while you're also taking certain other medications. Examples of medications to avoid include other antidepressants, certain pain medications such as tramadol and meperidine, over-the-counter decongestants, St. John's wort, and over-the-counter or herbal weight-loss products. Always check with your doctor or pharmacist before taking any new prescription medication, over-the-counter medication or supplement while taking MAOIs.

A rare but potentially life-threatening side effect of MAOIs is serotonin syndrome. This condition, characterized by dangerously high levels of serotonin in the brain, can occur when an MAOI interacts with another type of antidepressant called selective serotonin reuptake inhibitors (SSRIs). Because of this, don't take any MAOIs while you're taking any SSRIs or within two weeks of each other. Serotonin syndrome requires immediate medical treatment.

Signs and symptoms of serotonin syndrome include:

• Confusion
• Restlessness
• Hallucinations
• Extreme agitation
• Fluctuations in blood pressure
• Increased heart rate
• Nausea and vomiting
• Fever
• Seizures
• Coma

In some cases, antidepressants may be associated with worsening symptoms of depression or suicidal thoughts or behavior, particularly early in treatment or when you change your dosage. Be sure to talk to your doctor about any changes in your symptoms. You may need more careful monitoring at the beginning of treatment or upon a change in treatment, or you may need to stop the medication if your symptoms worsen.