And the adjustment struggle was more profound for National Guard troops and reservists than it was for active-duty soldiers.
About 42 percent of the Guard and reserves, compared to 20 percent of active-duty troops, were identified as needing mental health treatment in two screenings. The first testing was immediately upon return from Iraq and the second six months later.
Problems showed up more often on the second screening. From the time they returned, there was a fourfold increase in interpersonal problems, for example, likely driven by family conflicts as the returning soldiers adjusted to home life.
Almost a third of the more than 88,000 returning soldiers in the study had signs of depression, post-traumatic stress disorder, conflicts in relationships or other problems after six months.
That compared to about 17 percent when the soldiers first got home, according to the report that appears in Wednesday's Journal of the American Medical Association.
"We're trying to study these mental health impacts as the war unfolds and we're trying to apply what we're learning to set up new systems of care," said Dr. Charles Milliken of the Walter Reed Army Institute of Research, who led the study.
Questions about alcohol, which were only on the second questionnaire, found that 12 percent of active-duty soldiers and 15 percent of National Guard and Reserve soldiers said they were having drinking problems six months after returning home.
But alcohol treatment was rare. Of more than 6,600 active-duty soldiers with drinking problems, only 134 were referred for treatment and only 29 were seen within 90 days, the study found.
"We still have some work to do. The referral rate was low," Milliken said.
Alcohol treatment in the military is not confidential; in fact, it triggers the automatic involvement of a soldier's commander. That may explain the small percentage getting help, Milliken said.
Iraq veterans are being screened for mental health problems earlier and more often than previous vets. Shortly after starting the ground war in Iraq in 2003, the Pentagon began requiring returning troops to complete a three-page survey that is used to decide who needs help.
Among other things, the veterans are asked if they have nightmares, are constantly on guard or easily startled, and whether they feel numb or detached from others.
In the new study, the higher rates of problems reported by the Guard and reserves may reflect a need to document problems so treatment can be paid for by the military or Veterans Affairs, Milliken said.
For those citizen soldiers, the military's Tricare health insurance benefits expire after six months; VA benefits expire two years after a soldier's return to civilian status.
A report released in June said more money and people are needed to care for troops suffering mental health problems because of their war experiences. It also said the Pentagon needs to build a culture of support in the military to help remove the stigma of seeking psychological help.
Brig. Gen. Stephen L. Jones, an assistant surgeon general, said the military is making headway on that front.
The Army has created a training program called Battlemind that helps troops and families prepare for the stress of war and what signs of trouble to watch for.
"We're teaching our soldiers that seeking care is a sign of strength not of weakness," Jones said.