A wearable wristband that records motion 24 hours a day may be an inexpensive, safe way to determine which depression will benefit from commonly prescribed drugs such as Prozac.

Selective serotonin reuptake inhibitors, or SSRIs, are standard drugs used to treat depression, but patients often go through many months, doses, and different SSRIs before finding the most effective medications, noted W. Vaughn McCall, M.D., chairman of the Department of Psychiatry and Health Behavior at the Medical College of Georgia at Georgia Regents University.

"You only hit a home run first at bat about one third of the time; two-thirds of the time you have failed, struck out," said Dr. McCall, an expert on depression, insomnia, and suicide.

But a new study led by Dr. McCall, published in the Journal of Psychiatric Research, indicates that the simple wristband may help identifying those patients commonly referred to as "night owls," who stay up at night and appear to benefit most from SSRIs.

The study was small — involving 58 patients — but promising, he said.

"What our findings suggest is that night owls, the group most likely to be depressed, also look like the patients who are most likely to respond," Dr. McCall said.