PHOENIX - Researchers at the University of Arizona report they've found little credible research showing marijuana is effective in treating post-traumatic stress disorder.
Ditto for migraines, depression and general anxiety disorder, said the doctors from the school's College of Public Health.
And those findings - or, more to the point, the lack of findings - could prove to be a fatal blow to efforts by some to expand the list of ailments for which a doctor in Arizona can legally recommend marijuana. State Health Director Will Humble, who gets the final word, said he expects to make his decision by the end of the month.
The reports are an outgrowth of the 2010 voter-approved law allowing the use of marijuana by patients suffering from a list of several specified medical conditions. These range from glaucoma and AIDS to any chronic or debilitating condition that leads to severe and chronic pain.
With a doctor's recommendation, patients can get a card from the state allowing them to obtain up to 2 1/2 ounces of marijuana every two weeks. So far the state has issued almost 31,000 of these cards.
The 2010 law, though, requires Humble to regularly consider requests for expanding the list of conditions for which marijuana can be recommended.
Proponents submitted requests for four new conditions. Humble heard hours of testimony from those who said they are afflicted, along with how marijuana, used by many now without legal permission, has helped.
Backers also submitted everything from news and magazine articles to what they claimed was scientific backing.
But Humble said state law requires something more substantial for him to expand the list. And that, he said, means full-blown, double-blind, peer-reviewed scientific studies.
So Humble contracted with the UA to review all the information that is out there and see if there is anything credible.
The researchers found precious little.
Looking at PTSD, for example, they rated most of the studies of "very low quality."
Among the problems were not only the small size of many of the studies, but also that participants were "self-selected" as opposed as being drawn at random from the population at large.
They did find one study they rated as being of moderate to high quality. But the researchers said they found no studies at all that actually researched the benefit or harm of marijuana use among those with post-traumatic stress disorder. Similarly, they found only two systematic reviews that directly attempted to explore the association between depression and marijuana use.
"Both reviews were of low quality," the researchers said.
They said there is "conflicting evidence" about whether marijuana use and various forms of anxiety are related. Among the problems is the question of whether anxiety causes marijuana use or even that marijuana use causes anxiety.
Nor could researchers find credible reports on the issue of marijuana and migraines.
Humble said that while the UA reports are helpful, he still wants to discuss the findings with his staff before issuing a final ruling.
He said the lack of research supporting the theory that marijuana is helpful in treating the conditions is only part of the problem. The health director said he wants to make sure allowing patients to use marijuana does not make matters worse.
And that fear, he said, is complicated by the fact that the 2010 law only allows him to add to the list of conditions. Humble said there are no provisions for shrinking the list if subsequent research shows that marijuana use actually would be detrimental.
Humble said he has another concern: He does not want to be in a position of essentially allowing patients with some serious conditions to self-medicate with marijuana rather than getting treatment to deal with an underlying condition that is causing a problem like depression in the first place.