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Phenelzine is a drug licensed for the treatment of depression in adults. By blocking the action of monoamine oxidase in the brain, the medication can help improve the symptoms of depression. However, since there are many potentially dangerous food and drug interactions, it is usually only prescribed when other treatments have failed. Possible side effects include drowsiness, insomnia, and fatigue.

What Is Phenelzine?

Phenelzine sulfate (Nardil®) is a prescription medication that is used to treat depression (also known as major depression or clinical depression). Because this medication has numerous potentially lethal drug and food interactions, it is often used as a last resort, when other antidepressants have failed.
(Click What Is Phenelzine Used For? for more information, including possible off-label uses.)

Who Makes This Medication?

Phenelzine is made by Pfizer, Inc.

How Does It Work?

Phenelzine belongs to a class of medications called monoamine oxidase inhibitors (MAOIs).
To better understand how these medications work, it's important to understand how brain cells communicate with each other. Monoamines are special chemicals that carry messages from one brain cell to another. These messages can include information about many things, including your emotions. Examples of the monoamines that help transmit these messages include:
  • Dopamine
  • Norepinephrine
  • Epinephrine
  • Serotonin
  • Melatonin
  • Histamine.
When a message (electrical impulse) reaches the end of one brain cell, monoamines are released into the gap between the cells. Here, they quickly travel across the gap until they reach a receptor on the next cell, settling in like a key in a lock. This triggers the electrical impulse to continue through the next cell and on to its final destination.
Once the message has been transmitted, the monoamines in the gap are either reabsorbed by the first cell or broken down by an enzyme called monoamine oxidase.
If a person has low levels of monoamines in the brain, it can reduce the amount of communication between the brain cells and cause the person to feel depressed. MAOI medications improve the communication between brain cells by blocking the action of monoamine oxidase. This increases the amount of monoamines in the brain and, thus, improves a person's depression.
Unfortunately, monoamine oxidase is also responsible for breaking down tyramine, a naturally occurring chemical that affects blood pressure. MAOI medications keep the body from breaking down tyramine and can cause a person's tyramine levels to be too high (which can be extremely dangerous). Because this substance is found in many foods and beverages, people taking MAOI medications must follow a strict diet (see Nardil Food Interactions for more information).
Written by/reviewed by:
Last reviewed by: Kristi Monson, PharmD;
Last updated/reviewed:
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