antidepressant, any of a wide range of drugs used to treat psychic depression. They are given to elevate mood, counter suicidal thoughts, and increase the effectiveness of psychotherapy. Before the introduction of such drugs in the late 1950s, most patients with major depression had no recourse but hospitalization; only 45% improved after one year. In contrast, 80%-90% of such patients can expect significant relief from depression with one of the medications now prescribed. Antidepressants act on the flow of the neurotransmitters epinephrine, serotonin, and norepinephrine across neural synapses.

Common antidepressants include monamine oxidase inhibitors (MAOIs) such as isocarboxazid (Marplan), tricyclics such as imipramine (Tofranil) and amitriptyline (Elavil), and the newer selective serotonin reuptake inhibitors (SSRIs) as fluoxetine (Prozac) and sertraline HCL (Zoloft). Venlafaxine (Effexor) inhibits both serotonin and norepinephrine reuptake. The choice of antidepressant often has more to do with its side effects (variously sedation, constipation, hypotension, tachycardia, weight gain, sexual dysfunction) than efficacy, as they are generally regarded to be equally effective. The newer drugs, especially SSRIs, are tolerated better and are currently by far the most widely prescribed, but SSRIs also appear to be less effective in children and teenagers and may cause some of them to become suicidal.

Any drug used to treat depression. The three main types inhibit the metabolism of serotonin and norepinephrine in the brain. The aim is to keep these monoamine neurotransmitters from dropping to levels associated with depression. The drugs may take a few weeks to show any effect. Tricyclic antidepressants, which inhibit inactivation of norepinephrine and serotonin, help more than 70percnt of patients. Monoamine oxidase (MAO) inhibitors apparently block the action of MAO, an enzyme that helps break down norepinephrine, serotonin, and dopamine in neurons. They have unpredictable side effects and are usually given only when tricyclic drugs do not help. Selective serotonin reuptake inhibitors (SSRIs) apparently block reabsorption only of serotonin, allowing its levels to build up in the brain. SSRIs, which include fluoxetine (trade name Prozac), often help with depression unrelieved by tricyclics or MAO inhibitors and have milder side effects.

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