An already-approved muscle relaxant may offer relief for U.S. military veterans and first responders suffering from combat-related post-traumatic stress disorder (PTSD). The Phase 2 trials of the drug, TNX-102 SL, which contains the same chemical property as Flexeril, identified a dose and administration method that statistically improved participants PTSD symptoms among several mental health indices.

The findings were announced this month at the American Society of Clinical Oncology (ASCO) annual conference, and could eventually lead doctors to unroll the first PTSD drug in more than a decade, said principal investigator Dr. Harry Croft, a former U.S. Army psychiatrist. Croft, who has also headed the investigation of 60 similar clinical trials over the last 25 years, said current PTSD treatments either dont address every individuals range of PTSD symptoms, pose unwanted side effects, or have poor adherence rates. Thus, scientists have continued searching for new PTSD treatments.

The suffering caused by this condition is significant, not just for the veteran but for their family members, Croft, medical director of the San Antonio Psychiatric Research Center, one of 24 U.S. research sites for the drug, told FoxNews.com. Were hopeful that were on the right track with this medication.

New PTSD treatments: Whats the holdup?

U.S. combat servicemen and women serving in the Iraq and Afghanistan wars are the first in American history to be discharged multiple times, and soldiers today are more likely to suffer from PTSD than they are to get injured or die in combat. It was only after American soldiers returned from the Vietnam War that scientists coined the term PTSD, formerly referred to as shell shock an effect the military simply associated with a lack of masculinity or patriotism.

In World War I, soldiers who presented trauma-related were executed by firing squad for perceived cowardice, said Stephen Stahl, a psychiatry professor at the University of California, San Diego.

Today, although PTSDs pathology continues to mystify scientists, studies link the disorder with an increased risk of depression, anxiety and suicide. According to the National Institutes of Health (NIH), PTSD affects about 7.7 million American adults, including about 20 percent of Iraqi war veterans and about 11 percent of Afghanistan war veterans.

The Department of Veterans Affairs (VA) and the Department of Defense (DoD) have poured hundreds of millions of dollars into PTSD research, and are conducting brain imaging and biomarker studies, Ndidi Mojay, a VA spokeswoman, told FoxNews.com in an email. Researchers with the agencies have also established a database to monitor, identify risks for, and prevent suicide among the population, she added.

However, no new PTSD drug has been approved by the Food and Drug Administration (FDA) since Paxil in 2001, and before that, Zoloft in 1999.

Those drugs cause sexual dysfunction in up to 60 percent of patients, Croft said, and other drugs like selective serotonin reuptake inhibitors (SSRIs) address just individual PTSD symptoms, like depression. Meanwhile, cognitive behavioral therapy, a common treatment for PTSD, has only a 50 percent adherence rate, possibly because its mechanism is counterintuitive. One of the symptoms of PTSD is avoidance, which means a conscious effort to not want to talk about it or be around anything that exposes you to it, whereas cognitive behavioral therapy forces you to do that, Croft said.

Demonstrating a drugs efficacy in a military setting has proven difficult for scientists because veterans experiences at war arent limited to single instances of trauma, Croft said.

Stahl, also the director of psychopharmacology of California Department of State Hospitals who has consulted with the U.S. Army on PTSD, said poor study design and persistent attitudes about PTSD in the military may also be to blame.

Ive been an outspoken critic of saying that the VA says this is a vets problem and wants to defer this, Stahl said. The sweet spot of treatment may very well be as close to experiencing the trauma, Stahl said.

The drug Crofts team studied, TNX-102 SL, was administered to participants six to seven years after their PTSD-producing traumatic incident.