Antidepressant is the name of a group of drugs commonly used to treat major depression, a severe mental illness. Antidepressants also help treat other disorders, including chronic pain, anxiety disorders, and obsessive-compulsive disorder
Antidepressants are thought to work by regulating the brain's neurotransmission system. Chemicals called neurotransmitters carry messages from one nerve cell in the brain to another. These chemicals attach to special molecules on nerve cells called receptors, both in sending and receiving messages. Antidepressants first increase the concentration of neurotransmitters in the brain. After several weeks of treatment, the receptors become less sensitive, and depression lifts.
The three main types of antidepressants are (1) selective serotonin re-uptake inhibitors (SSRI's), (2) tricyclic antidepressants (TCA's), and (3) monoamine oxidase inhibitors (MAOI's). SSRI's and TCA's prevent brain cells from reabsorbing excess neurotransmitters after the chemicals have delivered their messages. SSRI's block the reabsorption of the neurotransmitter called serotonin. SSRI's include the most widely prescribed antidepressant, fluoxetine (Prozac). TCA's, such as the drug amitriptyline (for example, Elavil), block the reabsorption of several neurotransmitters, including serotonin and norepinephrine. MAOI's, which include the drug phenelzine (Nardil), inactivate a protein that breaks down excess neurotransmitters.
Excerpt from the "Antidepressant" article, The World Book Encyclopedia © 1999