Everyone experiences variation in mood. When we suffer personal loss, become ill, or experience a failure, we are likely to feel sadness and may say that we are depressed. Such variations are normal, add to the richness of our life experience, and may provide impetus for us to reassess personal values, goals, or make important life changes.
Many individuals, however, experience periods of depressed mood which are so severe or prolonged that they seriously impair their ability to function. Psychiatrists distinguish such episodes as qualitatively distinct from normal sadness and refer to them as major depression. Few suffering a serious major depressive episode would dispute that they are experiencing something which is abnormal, threatens their ability to function, and feels like an "illness" rather than an expected reaction to life events.
We now understand that such major depressive episodes reflect disturbance in brain function which are often described as a "chemical imbalance." In fact, both neurotransmitter (chemical) and neurophysiological (electrical) changes are involved. As if to remind us that the brain is part of the body, depression not only alters our feelings and perceptions, it can effect our memory concentration, sleep patterns, appetite and weight, sexual function, and physical activity.
Since depression is a physical illness, it might be reasonable to expect that a physician could do a laboratory test to diagnose depression, like we can with many other illness. Unfortunately, this is not currently possible. In spite of intensive research, we have not been able to develop any reliable tests which allow us to diagnose depression in a normal clinical setting. There are a variety of reasons for this. Mood is regulated partly by the action of neurotransmitter molecules in very tiny spaces between nerve cells called synapses. These chemicals do not enter the blood stream, and even if we could perform spinal taps on everyone, their concentrations in cerebral spinal fluid does not reflect their activity in the synapse. In addition, the brain is overwhelmingly complex; there are more connections between nerve cells in a single person than there are stars in the universe.
As a result, we are forced to fall back on symptoms to help us diagnose clinical depression. This is not as bad as it sounds. A very solid body of scientific research has identified a cluster of symptoms (called diagnostic criteria) which characterize the illness of depression, distinguish it from other conditions, and predict the probability of a respond to an antidepressant medication.
These criteria are listed on the DSM-IV Diagnostic Criteria page.
Major depression is surprisingly common. Approximately one out of every 6 or 7 individuals will experience an episode of major depression at some time during their life. Untreated, most episodes of major depression will persist for six months or longer. Usually, the illness resolves completely and there is a complete return to normal function. However, a small number of cases of major depression (perhaps 5%-10%) will last for a number of years. In addition, some cases of major depression (perhaps 20%-30%) will resolve only partially with residual symptoms that persist for years and cause some continued stress and disability.
Psychotherapy can be very helpful in the treatment of depression. In fact, psychotherapy alone may be as effective as medications alone in the treatment of mild to moderately severe depression. There is also a substantial body of evidence suggesting that the combination of medication and psychotherapy is more effective than either alone. Not suprisingly, the social withdrawal and poor self esteem associated with depression may be more responsive to psychotherapy, while physiological symptoms such as sleep and appetite disturbance may be more responsive to medications. It is also important to recognize that psychotherapy may be beneficial in ways not easily measured, for instance by facilitating psychological growth and the understanding of the self.
Antidepressant medications are effective and safe in the treatment of clinical depression, as substantiated by a large body of scientific evidence. This evidence includes many well controlled, double-blind, prospective clinical trials of the sort required to demonstrate that treatment is more effective than the placebo. In the treatment of uncomplicated major depression, improvement can be demonstrated in about 60% or 70% of individuals receiving their first trial of an antidepressant medication. The placebo rate is relatively high, and about 30% of individuals will report substantial improvement when recieving an inert substance with no physiological activity. Unlike the medication effect, it appears that the placebo effect is short lived, and disappears after a month or so.
We now have available about two dozen different medications which may be used in the treatment of depression, These include the serotonin-specific reuptake inhibitors (SSRI's), the tricyclic antidepressants (TCA's), atypical antidepressants, stimulants, anticonvulsants, and other mood stabilizers. See the individual web pages for discussion of these different classes of agents. There are two effective physiological treatments for depression which do not require the use of medications: electroconvulsive therapy (ECT) and bright-light therapy.
Most of the commonly used antidepressants have about the efficacy in treating uncomplicated depression, However, there is good evidence that some individuals will respond better to some antidepressants than others. For instance, people who respond well to SSRI's are likely to respond more poorly to TCA's, and vice versa. Unfortunately, there is no way to tell for sure which medication will be the best for a particular individual. Because they are effective for depression, anxiety social phobia, and several other conditions, and because they are safe and well tolerated, the SSRI antidepressants are most commonly used as first line drugs.
Many people wonder how long they will need to continue antidepressants if their depression improves. Antidepressants not only treat episodes of depression, they also prevent recurrences. Individuals experiencing their first ever major depressive episode are about 40% likely to have another episode at some point during their life. After the second major depression, this goes up to about 60% or 70%. People who have had 3 major depressive episodes are over 90% likely to have at least one more episode. Major depression is very disruptive to peoples lives, has great economic cost, and can result in suicide. On the other hand, the long term use of antidepressant medications appears to be quite safe without cumulative damage or side effects. Given these facts, most psychiatrists are recommending that people who have had 3 or more episodes of clinically significant depression consider lifelong use of antidepressants. In any case, it appears that the chance if recurrence of depression is increased if the medications are discontinued too soon or too quickly, so if effective, they should probably be continued at least 6 months and tapered slowly (over at least 1-2 weeks).