Servicemembers with 1st Marine Logistics Group participate in a five-day Operational Stress Control and Readiness Program, a course designed to help Marine and sailors identify and help fellow servicemembers with stress. Related Stars and Stripes coverage of PTSD

A leading cause of post-traumatic stress disorder is guilt that troops experience due to moral dilemmas faced in combat, according to preliminary findings of a study of active-duty Marines.

The conflicts that troops feel can range from survivor guilt from living through an attack where other troops died, to witnessing or participating in the unintentional killing of women or children, researchers involved in the study say.

"How do they come to terms with that? They have to forgive themselves for pulling the trigger," says retired Navy captain Bill Nash, a psychiatrist and study co-author.

The idea of "moral injury" as a cause of PTSD is new to psychiatry. The American Psychiatric Association is only now considering new diagnostic criteria for the disorder that would include feelings of shame and guilt, says David Spiegel, a member of the working group rewriting the PTSD section.

Traditionally, PTSD symptoms such as nightmares or numbness to the world have been linked to combat violence, fear of being killed or loss of friends.

Half of all Iraq and Afghanistan veterans treated by the Veterans Affairs have been diagnosed with mental health issues and the most common is PTSD, which is experienced by nearly 200,000 of these veterans, according to the VA.

PTSD caused by moral injury can lead to more severe reactions such as family violence or even suicide, says Jonathan Shay, a psychiatrist who has worked on military mental health policies.

The Marine Corps study helps expand the knowledge of the relationship between moral injury and PTSD, says Shira Maguen, a psychologist and VA researcher who has studied links between killing and the disorder among Vietnam, Gulf War and Iraq War veterans.

"This (Marine Corps) study is important because so little work has been done to understand moral injury in a scientific context," Maguen says.

The ongoing research involves about 2,600 Marines and sailors examined before and after combat tours.

The preliminary findings on moral injury were gleaned from 208 Marines involved in severe combat in Afghanistan in 2009 and 2010. It showed that three months after coming home, 7% of the Marines likely had PTSD. Their condition was more closely linked to an inner conflict rather than threats to their lives, the sight of bodies or blood or family problems, the study said.

