How Do MAO Inhibitor Antidepressants Work?

Monoamine oxidase (MAO) inhibitor antidepressants are medications prescribed to treat depression. MAO inhibitors improve mood by increasing the concentration of chemical substances (neurotransmitters) released by nerve cells (neurons) in the brain, which include dopamine, serotonin, epinephrine, and norepinephrine.

Neurotransmitters are chemical messengers that regulate physiological functions such as breathing, heart rate, and digestion, and are also responsible for learning, memory, sleep, emotions, and behavior. Neurotransmitters are normally broken down and reabsorbed by the neurons after the transmission of neural signals.

Monoamine oxidase is an enzyme that is responsible for the breakdown of neurotransmitters. MAO inhibitors block the activity of monoamine oxidase, which results in an increase in neurotransmitter levels in the brain.

MAO inhibitor antidepressants are oral tablets approved by the FDA for the treatment of the following conditions:

• Major depressive disorder
• Major depressive episode with melancholia

Side effects of MAO inhibitor antidepressants may include the following:

• Orthostatic hypotension (blood pressure drop when standing up from sitting or lying down)
• Dizziness
• Somnolence (drowsiness)
• Fatigue
• Headache
• Hyperreflexia (overreactive reflexes)
• Sleep disturbance
• Asthenia (weakness)
• Tremor
• Constipation
• Dry mouth
• Weight gain
• Confusion
• Decreased memory
• Paresthesia (prickling sensation)
• Anorexia (loss of appetite)
• Nausea
• Vomiting
• Nystagmus (involuntary eye movement)
• Urinary frequency or retention
• Impotence
• Elevated liver enzymes
• Edema
• Anxiety
• Hypomania
• Irritation
• Hypermetabolic syndrome, a condition with an increased metabolic rate that causes symptoms such as:
  • Hyperpyrexia (extremely high temperature)
  • Tachycardia (rapid heart rate)
  • Tachypnea (rapid and shallow breathing)
  • Increase in creatine phosphokinase (CPK) levels
  • Acidosis (excessive acid in body fluids)
• Syndrome of inappropriate antidiuretic hormone secretion (SIADH, a disorder which causes water retention)
• Arthralgia (joint pain)

Rare side effects:

• Risk of hypertensive crisis (usually due to drug interaction)
• Ataxia (impaired coordination)
• Seizure
• Jaundice
• Visual disturbance
• Worsening depression
• Suicide
• Edema of the glottis (vocal cords)
• Leukopenia (low blood count of leukocytes, a type of immune cells)
• Hepatic necrosis (injury to the liver)
• Drug-induced lupus erythematosus (an autoimmune inflammatory disease)

Information contained herein is not intended to cover all possible side effects, precautions, warnings, drug interactions, allergic reactions, or adverse effects. Check with your doctor or pharmacist to make sure these drugs do not cause any harm when you take them along with other medicines. Never stop taking your medication and never change your dose or frequency without consulting your doctor.

Generic and brand names of MAO inhibitor antidepressant drugs include:

• isocarboxazid
• Marplan
• Nardil
• Parnate
• phenelzine
• tranylcypromine