As their name suggests, mood disorders are characterized by disturbances in mood or prolonged emotional state, sometimes referred to as affect. Most people have a wide emotional range – that is, they are capable of being happy or sad, animated or quiet, cheerful or discouraged, overjoyed or miserable, depending on the circumstances. In some people with mood disorders, this range is greatly restricted. They seem stuck at one or the other end of the emotional spectrum – either consistently excited and euphoric or consistently sad – whatever the circumstances of their lives. Other people with a mood disorder alternate between the extremes of euphoria and sadness.

The most common mood disorder is depression, a state in which a person feels overwhelmed with sadness, loses interest in activities, and displays other symptoms such as excessive guilt or feelings of worthlessness. People suffering from depression are tired and apathetic unable to experience pleasure from activities they once enjoyed. Frequently unable to make the simplest everyday decisions, they may feel as if they have failed utterly in life, and they tend to blame themselves for their problems. Seriously depressed people often have insomnia and lose interest in food and sex. They may have trouble thinking or concentrating – even to the point of finding it difficult to read a newspaper. In very serious cases, depressed people may be plagued by suicidal thoughts or even attempt suicide.

It is important to recognize the difference between clinical depression and the “normal” kind of depression that all people experience from time to time. It is entirely normal to become sad when a loved one has died, when you've come to the end of a romantic relationship, when you have problems on the job or at school – even when the weather's bad or you don't have a date for Saturday night. Most psychologically healthy people also get “the blues” occasionally for no apparent reason. But in all these instances, the mood disturbance is either a normal reaction to a “real-world” problem (for example, grief) or passes quickly. Only when depression is serious, lasting, and well beyond the typical reaction to a stressful life event is it classified as a mood disorder.

The DSM-IV distringuishes between two forms of depression. Major depressive disorder is an episode of intense sadness that may last for several months; by contrast, dysthymia involves less intense sadness (and related symptoms) but persists with little relief for a period of 2 years or more. Some theorists suggest that major depressive disorder is generally caused by a difficult life event, whereas dysthymia has its roots in a physiological disorder, but this is just speculation at this time. It is true, however, that some depressions can become so severe that people become psychotic – that is, they lose touch with reality.

Depression occurs two to three times more frequently in women than in men.

1. Understanding Psychology: 3^rd Edition. Charles G. Morris.