It is thought that depression is predominantly caused by insufficient levels of monoamine neurotransmitters in the brain, and this theory is supported by antidepressant drug treatment. Signals from the brain are transported by neurotransmitters across the gap (synaptic cleft) between nerve cells. Antidepressants increase the concentration of one of these neurotransmitters in the "gap" (e.g., SSRIs increase concentrations of serotonin). Sustained levels of neurotransmitters improves neurotransmission, which improves and elevates mood.

Antidepressants improve sleep and appetite, reduce anxiety, sharpen concentration, and restore energy levels. They are most effective in patients who have responded well to medication in the past, and who suffer from associated conditions such as anorexia and insomnia. A history of nonreaction to medication, personality disorder, delusions, psychosis, and chronic depression may indicate a poor response to medication.

Because people suffering from depression experience little or no sense of reward, they eventually may discontinue participation in activities that had been rewarding in the past. Unproductiveness, disinterest, and depression are often the result. Antidepressant medications increase the levels of monoamine neurotransmitters (i.e., serotonin, dopamine, norepinephrine) to elevate mood and restore a sense of well-being.

Antidepressants may take 1–8 weeks to be effective, depending on the dosage and on the patient. Most physicians begin therapy at a low dosage, and patients who have difficulty adjusting to the drug may be treated with an even lower dose. In most cases, the dosage is gradually increased as the patient's tolerance and response to the drug increases. An effective concentration of the drug in the body must be attained before the patient experiences the desired results.

Side Effects of Antidepressants

Because available medications may take several weeks to take effect, patients commonly experience side effects before they experience benefits. The abrupt discontinuation of antidepressant medication is not recommended. The dosage is gradually tapered to avoid the intensification of side effects and "rebound effect," that is, a sudden onset of a severe depressive episode.

Publication Review By: the Editorial Staff at

Published: 03 Feb 2001

Last Modified: 11 Sep 2013