THURSDAY, Aug. 24 (HealthDay News) -- Two widely used antidepressants, nortriptyline and Zoloft (sertraline), are safe and effective for treating postpartum depression, a new study finds.

The University of Pittsburgh study is one of the first to compare the effectiveness of two classes of antidepressants -- a selective serotonin reuptake inhibitor (Zoloft) and a tricyclic (nortriptyline) -- in treating the common, debilitating condition.

"We've been treating postpartum depression based on the assumption that drugs that work for a woman with depression under usual circumstances, will work for a women who experiences depression after giving birth, but there have not been studies that provide scientific proof that this was an effective and safe course of treatment," Dr. Katherine L. Wisner, professor of psychiatry and obstetrics, gynecology and reproductive sciences at the University of Pittsburgh School of Medicine, said in a prepared statement.

The study started with 109 participants, randomly selected to take either nortriptyline or Zoloft. Of those 109 women, 95 provided response data at four weeks, 83 provided data at eight weeks, and 29 completed between 20 and 24 weeks of the study.

Both drugs produced similar results.

By week four, 46 of the participants taking Zoloft had responded with a reduction in depressive symptoms and 27 percent had remitted (few depressive symptoms), while 56 percent of those taking nortriptyline responded and 30 percent remitted.

Of the 29 women who remained in the study until 20 to 24 weeks, 93 percent taking Zoloft responded and 73 percent remitted, while 100 percent taking nortriptyline responded and 79 percent remitted.

Both drugs produced similar improvements in psychosocial functioning, and neither drug was superior to the other in treating aggressive obsessional thoughts, the study said.

The findings were published in the August issue of the Journal of Clinical Psychopharmacology.

The Zoloft used in the study was donated by the drug's maker, Pfizer, but the drug company did not provide any direct financial support for the study, which was funded by the U.S. National Institutes of Health.

Wisner is a member of Pfizer's speaker's bureau and has a grant from Pfizer to study one of its other products. Wisner is also a member of the speaker's bureau for GlaxoSmithKline.