WASHINGTON — Researchers who are trying to determine whether marijuana works to treat post-traumatic stress disorder enrolled their final veteran needed for the study on Veterans Day.

The Scottsdale Research Institute in Phoenix, which is performing the study, achieved its total enrollment nearly two years after they first began recruiting veterans into the study – and eight years since the Food and Drug Administration approved it.

“A nearly 10-year saga for this PTSD-cannabis study,” lead researcher Sue Sisley wrote in an email. “Almost at [the] finish line.”

The study is the first government-approved research into marijuana’s effects on PTSD. When it’s done, Sisley aims to have a definitive answer of whether marijuana benefits people with PTSD, and if there are negative consequences.

All of the study’s participants are veterans.

Once researchers began recruiting veterans for the study in February 2017, they immediately ran into problems. By September 2017, they had screened thousands of veterans but enrolled only 26 who met the eligibility criteria.

For a while, there were concerns the study would have to broaden to include non-veterans.

At issue was the researchers’ lack of access to the Department of Veterans Affairs hospital in Phoenix, just 20 miles from where the study is being conducted. Sisley saw potential there to find a large group of veterans who might be resistant to other PTSD treatments and looking for an alternative.

The VA said federal law restricted the agency from researching medical marijuana or referring veterans to projects involving the drug.

“Despite the refusal of the [VA] and Arizona’s public universities and hospitals to assist with recruitment for the study, the trial is on track to finish on time,” read a news release from the nonprofit Multidisciplinary Association for Psychedelic Studies, which is sponsoring the research.

To enroll, veterans had to be diagnosed with chronic PTSD brought on by military service. Researchers wanted a range of ages, as well as men and women. The study needed 76 veterans to be viable.

It’s a random, controlled trial. The veterans participating are given 1.8 grams of marijuana each day of differing potencies. They choose how much to smoke, and they’re asked to keep a daily journal.

Participants visit Scottsdale Research Institute 17 times during 12 weeks, and then are scheduled for six-month follow-ups. Researchers intend to publish their findings sometime in 2019.

“Hopefully, we’ll be able to finally answer the question, ‘Does cannabis help with PTSD?’ That’s our goal,” Sisley said at the start of the study in 2017. “That’s why we’ve been fighting so hard to get this underway.”

More veterans have spoken out in favor of medical marijuana in recent years. The American Legion passed a resolution supporting the study, and the chairman of the House Committee on Veterans’ Affairs, Rep. Phil Roe, R-Tenn., also voiced his support for more research into the drug.

There are efforts in Congress to allow VA doctors to recommend marijuana to veterans in states where the drug is legal. Separately, a bipartisan group of lawmakers, including Roe, urged VA Secretary Robert Wilkie for the agency to conduct its own research into marijuana as a treatment for PTSD, chronic pain and other ailments that disproportionately affect veterans.

When asked about medical marijuana last week, Wilkie was adamant that the VA wouldn’t explore it as a potential treatment until the federal government makes marijuana legal.

“Marijuana is against the federal law,” he said Friday during an event at the National Press Club in Washington. “If the laws change and there’s medical evidence there, of course we look at that. But the law is pretty clear at the federal level.”

wentling.nikki@stripes.com

Twitter: @nikkiwentling