Troops returning home from Iraq or Afghanistan often suffer from post traumatic stress disorder. But the cause might not be limited to what troops experience on the battlefield.

Concussions are a war injury people don't hear about much. Army Sgt. 1st Class Andrew Brown remembered one he got two years ago in Iraq when an explosion knocked him back.

“A rocket landed between 50 and 100 feet from where I was,” he said.

Doctors at Walter Reed Army Institute say concussions can have a lasting effect.

“Those soldiers had a much higher rate of post traumatic stress disorder,” said Dr. Charles Hoge.

In a new study, researchers found concussions are not only common, but up to 44 percent of soldiers who suffer one go on to develop PTSD. That includes Brown, who was diagnosed in 2006 after he returned home.

“There was depression. There was a couple of instances where I was more than ready to put a pistol in my mouth,” Brown said.

The psychological condition can also take a physical toll. Troops with PTSD “are at higher risk for using medical services, missing work due to illness, having pain or fatigue or other medical problems,” Hoge said.

While the finding sounds grim, there was a positive side to the discovery. Doctors said they can now track concussion victims more closely for signs of PTSD.

Experts say treating the traumatic stress can help physical ailments. Brown used to suffer fatigue and stomach problems. After working with a psychologist, he has improved mentally and physically.

“I'm not where I was three years ago prior to deployment. It's getting better. It's certainly getting better,” he said.