Mood, like color, has a range of hues, from the bright shades of happiness to the dark ones of depression. A mood problem that's down in the dark range, but doesn't quite reach the level of depression, is dysthymia (dis-THIGH-me-ah). It refers to a long-term drone of low-grade depression that lasts for at least two years in adults or one year in children and teens. While not necessarily as crippling as major depression, its persistent hold can keep you from feeling good and interfere with your work, school, family, and social life. Think of dysthymia as a dim gray compared to depression's blackness.

You might have dysthymia if you feel depressed during most of the day. You carry out your daily responsibilities, but without much zest for life. The depressed mood lingers for more than two months at a time, and is accompanied by at least two of these symptoms:

• overeating or loss of appetite
• insomnia or sleeping too much
• tiredness or lack of energy
• low self-esteem
• trouble concentrating or making decisions
• feelings of hopelessness

This low-grade depression lasts an average of five years. That's another way it differs from major depression, in which relatively short episodes can be separated by considerable spans of time. It's possible for an episode of major depression to occur on top of dysthymia; this is known as double depression.

Dysthymia often begins early in life, during childhood, the teen years, or early adulthood. Being drawn into this low-level depression tends to make major depression more likely. In fact, up to 75% of people who are diagnosed with dysthymia will have an episode of major depression within five years.

This low-grade depression doesn't usually fade away all by itself. Treatment, though, helps ease dysthymia and other depressive disorders in about four out of five people.

If you think you have low-grade depression, talk with your doctor. He or she may recommend that you see a mental health professional for the most effective approach: talk therapy combined with antidepressant medication.

For more information on treating depression, purchase Understanding Depression, a Special Health Report from Harvard Medical School.

Treating depression: take three steps

If we were all carbon copies of each other, identifying the causes of depression and its proper treatment would be simpler. But unique differences in life experience, temperament, and biology make treating depression a complex matter. No single treatment works for everyone. What works for many people, though, is a combination of talk therapy and medication.

Treatment is often divided into three phases. Keep in mind, though, that there are no sharp lines dividing the phases, and most people don't take a straight path through them.

Acute phase. The goal here is to relieve your symptoms. Generally, this occurs within four to eight weeks, but it may take longer depending on your response to the first treatments you try.

Continuation phase. During this period, you work with your doctor to maximize the improvement you've made. Further treatment adjustments, such as modifying the dosage of a medication, can help. This period can take four to five months.

Maintenance phase. Throughout the maintenance phase, your goal is to prevent depression from reemerging. Ongoing treatment is often necessary, especially if you have already experienced several depressive episodes, have chronic low mood, or have risk factors that make a recurrence more likely.

For more information on treating depression, purchase Understanding Depression, a Special Health Report from Harvard Medical School.