New research suggests that depression can significantly amplify the tendency for veterans with post-traumatic stress disorder (PTSD) to lash out in anger.

Among their subjects, American researchers found that PTSD was usually paired with depression. PTSD is a mental health condition that develops "after a terrifying ordeal that involved physical harm or the threat of physical harm," the National Institute of Health reported.

"Our study findings should draw attention to anger as a major treatment need when military service members screen positive for PTSD or for depression, and especially when they screen positive for both," Raymond Novaco, lead author of the study, said in a statement.

For the study, researchers collected and analyzed data from more than 2,000 U.S. soldiers who were deployed to Iraq and Afghanistan and subsequently sought behavioral health services at a large military installation. They were screened for PTSD and major depressive disorder (MDD), placing them in one of four groups: PTSD-only, MDD-only, PTSD and MDD combined or neither.

They found that anger and the risk of self-harm were higher in the group with both PTSD and MDD compared to the other three groups, which had just one of those disorders or neither. Around 72 percent

"Anger is a driver of violent behavior but it is responsive to anger-focused psychological treatment," Novaco said.

The findings are detailed in the journal Psychological Trauma: Theory, Research, Practice, and Policy.