A clinical trial is underway on the effectiveness of marijuana for treating Post Traumatic Stress Disorder (PTSD) in veterans.

The study was launched on Monday by the Multidisciplinary Association of Psychedelic Studies (MAPS), a non-profit research organization in California. According to officials, the study will focus on the effectiveness and safety of using marijuana at four separate potency levels.

NBC 7 spoke to some local veterans on Wednesday who said they hope that if the results are positive, medical marijuana could help thousands of veterans living with PTSD.

Kayla Carnevale, a Marine veteran served in Iraq in 2001, was diagnosed with PTSD by the VA.  She told NBC 7, she recently began using medical marijuana regularly at night and said it has changed her life.

"I feel good. I have a good night sleep and also I feel happier that I'm not waking up to bad nightmares as well," she said.

She added that prior to using medical marijuana, she would wake up in the middle of the night in "excruciating pain".

"They kept prescribing pill, after pill, after pill, after pill trying to figure out how to get rid of that and it was just as simple as the marijuana," she added.

Carnevale said she knows many veterans who served in combat who have PTS and they, like her, also have a medical marijuana card.

But the drug is not covered through the VA and can cost more than $100 a month.

"Not all veterans can afford that," she said.

A spokesperson with the San Diego VA medical center told us the VA cannot participate in marijuana research because they are banned by federal agencies. The VA has also been under pressure to prescribe less drugs, including pain killers because of addiction and overdoes issues.

The study will be conducted on 76 veterans in two locations--Phoenix, Arizona and Baltimore, Maryland.