Minor depression, the subset of major depressive disorder that affects upward of 15 million Americans, can be effectively treated with selective serotonin reuptake inhibitors, according to an article in the October issue of the American Journal of Psychiatry.

“This is especially important since patients with minor depression are not only at risk for significant psychosocial impairment, but for major depressive episodes that can be even more debilitating,” said the study’s lead author, Lewis L. Judd, MD.

He added that unclear categories of illness and diagnosis in the past have led psychiatrists to generally consider minor depression to be a negligible condition that didn’t require any treatment. Although some mental health professionals have considered minor depression to be a non-specific variation of normal mood, more recent studies have identified it as a clinically significant medical condition.

With the current opinion that minor depression can and should be treated, Judd said the new study of 162 patients with minor depressive disorder showed that patients given fluoxetine over a 12-week period showed significantly greater improvement in mood and psychosocial function than depressed patients who received a placebo. The Inventory of Depressive Symptomatology, Hamilton Depression Rating Scale, Beck Depression Inventory, the Clinical Global Impression severity scale, and the Global Assessment of Functioning Scale were used to compare results between groups.

The National Institute of Mental Health (NIMH) notes that, in addition to being a common disorder that can impair a person’s function and quality of life, minor depression is a serious risk factor for major depression. The difference between major and minor depression is the number of symptoms. Major depressive disorder includes the primary criteria of sadness plus at least five symptoms (such as insomnia, weight loss or gain, low energy, difficulty concentrating, reduction in sexual drive, suicidal ideas and/or behavior, psychomotor slowing, restlessness or irritability, inertia to initiate activity, and persistent physical symptoms, such as headache or digestive disorders, that don’t respond to treatment); minor depression includes the same primary sadness plus one or two additional symptoms.

Judd, a former director of the National Institute for Mental Health and a national expert on depression, said “Minor depression is the same as or a less severe variant of major depressive disorder. Significantly, it doesn’t reach the threshold of a major depression. In previous studies, we’ve seen that depressive symptoms wax and wane over an individual’s lifetime, with most depressed patients usually suffering from minor depression more of the time than major depression.”