PHOENIX — A University of Arizona doctor has been given approval from a key government agency to conduct studies that could put the school at the forefront of medical-marijuana research.

The Public Health Service has said Dr. Suzanne Sisley can proceed with her plans to study whether the drug, which remains illegal under federal law, could be used to treat people with post-traumatic stress disorder. Sisley said this would be the first-ever study of its kind.

That approval, which came late last week, is not the final hurdle. She still needs permission from the U.S. Drug Enforcement Administration.

Sisley said Monday that approval is largely contingent on the DEA concluding that the UA has made proper arrangements for ensuring that the drugs are being securely stored.

She has not yet received a response from the university. And requests for comment were not returned.

But UA lobbyists are clearly interested in the research: They were instrumental last year in crafting an exception for approved research to state laws banning medical marijuana on campus.

Sisley called the approval “a historic shift in policy and medical marijuana drug-development research.”

She said other programs approved by the Public Health Service and the National Institute for Drug Abuse, the agency that grows the marijuana for research, have generally been allowed when researchers have said they wanted to study the harmful effects of the drug. Sisley said her study is clearly meant to see if there are benefits.

The plan is for “randomized control tests” using about 70 patients who suffer from PTSD.

She said those participating will get doses ranging from a placebo to marijuana with 12 percent THC, the psychoactive ingredient in the plant. Some will get a mixture containing THC and another element from marijuana. She also wants to compare the results of those who smoke the drug with those who inhale it as a vapor .

Just getting to this point has taken years.

Sisley gained approval nearly three years ago from the U.S. Food and Drug Administration to conduct the study to see if the drug can be used to help combat veterans. It also has been blessed by the UA’s institutional review board, which must give the go-ahead for research on live subjects. Then, state law had to be amended to even allow her to bring the drug to campus.

But what really may have pushed the PHS and NIDA over the edge, she said, was Dr. Sanjay Gupta, the medical expert for CNN, concluding that opposition to research — including his own — made no sense.

That started last year with Gupta’s on-camera conclusion that he had been wrong. And he followed  just last week with a second televised story.

Sisley said that second report resulted in media inquiries to the federal agencies asking why they had not approved such studies. And while Sisley said she cannot say there was a direct connection, she got the go-ahead Friday to her long-pending application.

“Gupta was such a lightning rod,” she said. “When he had the guts to say, ‘I was wrong,’ people really took notice because that doesn’t happen very often that a physician would admit that they had misjudged this plant.”

Sisley said the delays by the feds have taken their toll. She said that more than 24,000 veterans have committed suicide since she got initial FDA approval for the study and has been waiting for the final go-ahead.

Sisley figures that it could take up to two years to complete the study and reach conclusions.

If she does find a benefit, Arizonans could be among the first to gain.

The 2010 voter-approved law that allows doctors to recommend marijuana to patients has a specific list of acceptable conditions. These range from things like HIV and AIDS to glaucoma. There also is a much-used catch-all of severe and chronic pain. But that list, which was prepared by the Marijuana Policy Project, does not include PTSD.

But that 2010 law required state Health Director Will Humble to accept petitions each year to add more medical conditions to the list.

Those who want to expand the list must provide a summary of evidence that marijuana will help a specific condition, along with “articles, published in peer-reviewed scientific journals, reporting the result of research on the effects of marijuana on the medical condition.”

Humble said that, to date, he has seen no such studies on marijuana and PTSD.

Sisley said her study should provide that evidence, paving the way for Humble to give the go-ahead. And she is confident that her study will show the benefits. Sisley figures she will need about 19 pounds of marijuana for her study, something she said should cost $60,000 at current NIDA prices.