DENVER (AP) — Colorado's decision not to allow marijuana to treat post-traumatic stress disorder has prompted a lawsuit by PTSD sufferers.

Five PTSD patients filed suit Thursday in Denver District Court. They're challenging a July decision by the Colorado Board of Health not to make PTSD the first condition added to Colorado's medical pot eligibility list in 15 years.

The PTSD rejection came despite a recommendation from Colorado's chief medical officer and a panel of physicians. They said that questions remain about how effective pot is as a PTSD treatment, but that people with PTSD are commonly using pot anyway and that the designation would allow for better understanding about how people are using the drug.

But the Board of Health cited insufficient federal research and denied the request on a 6-2 vote.

A lawyer for the PTSD patients, Bob Hoban, said the board applied an improper standard in its rejection.

"The board in effect established a standard that was impossible to meet," Hoban said. "They insist on having a federal study, which in effect is a futile standard."

Authorities have 21 days to respond to the complaint, which has no hearing date set. A spokeswoman for the Colorado Department of Public Health and Environment, which is also named in the lawsuit, declined to comment Friday.

Colorado allows adults over 21 to buy pot for recreational use, with no doctor's recommendation needed. But medical pot in Colorado is taxed at 2.9 percent, compared with at least 25 percent for recreational pot. Medical patients are allowed to possess twice as much marijuana — 2 ounces instead of 1 ounce.

Colorado had about 113,000 people on the medical marijuana registry in May, the most recent data available.

Patients seeking medical marijuana must get a doctor's recommendation to use it to treat one of eight debilitating conditions, including cancer, AIDS, chronic wasting diseases, glaucoma, seizures, persistent muscle spasms, severe pain and severe nausea. More than 93 percent of current patients list severe pain as their condition.

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Kristen Wyatt can be reached at http://www.twitter.com/APkristenwyatt