A Maryland senator has asked the Pentagon for information on how many troops in war zones have been prescribed antidepressants while they were deployed.

Democratic Sen. Ben Cardin sent a letter Tuesday to Defense Secretary Robert Gates expressing concern about how antidepressant drugs are being administered troops in Iraq and Afghanistan.

Cardin said he wanted to determine if the Defense Department is prescribing antidepressants appropriately and was concerned that there may be a connection between the use of those medications and the suicide rate among troops.

Cardin said the rate of active-duty suicides is greater than that of the U.S. population.