For the first time in history, a sizable number of U.S. combat troops are taking daily doses of antidepressants to calm nerves strained by repeated and lengthy combat tours.

Data from the army’s Mental Health Advisory Team report indicate that about 12 percent of combat troops in Iraq and 17 percent of those in Afghanistan are taking prescription antidepressants or sleeping pills to help them cope.

The survey probably underestimates antidepressant use. But even if the Army numbers are correct, they could mean that as many as 20,000 troops in all services in the two regions were on such medications last fall.

Troops have historically been barred from using such drugs in combat, and soldiers have usually been prescreened for mental illnesses before enlisting. The increase in the use of medication among U.S. troops suggests the heavy mental and psychological price being paid by soldiers fighting in Iraq and Afghanistan.

Military doctors have said that the drugs help to “conserve the fighting strength” of soldiers in combat. But at least one soldier, Sergeant Christopher LeJeune, said the drugs may be creating unfit soldiers.

"There were more than a few convoys going out in a total daze," LeJeune said.