Very little research has been done on minor depression, although it is quite common.  Patients usually don't get to psychiatrists unless than have major depression.  Also, drug companies prefer to research their medications on major depression, because the benefits are more likely to show up when the depression is more severe.

In my opinion, a long-lasting minor depression not clearly linked to an environmental factor should probably be treated with anti-depressant therapies.  At the present time, the treatment approach would be very similar to that for major depression.

Fluoxetine (Prozac) Helped Minor Depression: In a 12-week DB PC study of 162 patients with a minor depressive disorder, fluoxetine was superior to placebo for the Inventory of Depressive Symptomatology, the 17-item and 21-item Hamilton Depression Rating Scale, the Beck Depression Inventory, and the Clinical Global Impression severity scale. Randomized, placebo-controlled trial of fluoxetine for acute treatment of minor depressive disorder. Judd LL, Rapaport MH, et al. University of California, San Diego. Am J Psychiatry. 2004 Oct;161(10):1864-71

Sertraline (Zoloft) Not Helpful for Post-Stroke Depression: In a 26-week DB PC study of 123 post-stroke depressed patients (average age 70) at a mean of 128 days after stroke and either a diagnosis of major depressive episode (N = 76) or minor depressive disorder (N = 47), sertraline (50-100 mg/day) did no better for antidepressant effect and neurologic outcome except at week 6 (p < .05). At week 26, the improvement in QoL was better in sertraline patients (p < .05) and there was a trend for emotionalism (p = .07). Double-blind comparison of sertraline and placebo in stroke patients with minor depression and less severe major depression. Murray V, et al. Karolinska Institutet, Stockholm, Sweden. . J Clin Psychiatry. 2005 Jun;66(6):708-16