(CNN) More than half of US states allow for medical marijuana, and several states and the District of Columbia have legalized its recreational use.

Yet the use of marijuana in America's most popular professional sports league remains controversial. It's on the National Football League's banned substances list, but more and more players are calling for the league to reconsider its stance.

"I'm concerned about my health. I'm going on year seven playing in the NFL, and I think we need to know what the options are when it comes to taking care of our bodies," said Derrick Morgan, a linebacker with the Tennessee Titans.

Current, former players call for 'serious attention'

Morgan is the only current NFL player who has spoken out against the league's marijuana policy. He and eight former players co-signed a letter with Doctors for Cannabis Regulation , provided to CNN first, calling on the NFL to change its position.

The letter says, "cannabis deserves the serious attention of your medical staff as a viable pain management alternative and potential neuroprotectant."

"It's the responsibility of the medical professionals of the NFL to take this issue on and do something to potentially help players safety and help with their long term safety, " said former Baltimore Ravens offensive tackle Eugene Monroe, who retired this summer after seven seasons in the NFL.

He uses cannabidiol oil derived from marijuana's cousin, hemp. The oil contains CBD, the non-psychoactive chemical in marijuana, which is thought to have neuroprotective qualities , potentially heading off neurodegenerative diseases such as Alzheimer's and Parkinson's. Monroe also has a medical marijuana prescription to deal with the pain from his years of playing.

An alternative to opioids?

Like in much of the country, opioid addiction has taken root in the NFL. According to a 2011 study in the Journal of Drug and Alcohol Dependence , over half of all retired NFL players used narcotic painkillers during their careers, and 71% of those ended up abusing those painkillers. One in seven of those players continues to have dependency issues after playing.

"We should have all options available to us," Morgan said, when it comes to pain management.

"We know cannabis isn't 100% safe, but the meds that doctors administer to players every week is killing people across the country. Cannabis should be explored," he said.

NFL Commissioner Roger Goodell was asked last month whether the NFL would change its position on marijuana in light of the drug's legalization in a number of states. He replied, "Right now, it's not something that we're actively considering. Our doctors are always evaluating that. If they see they can improve our policies or what we can do better to protect our players or help our players, we'll look at it."

Players union looking into alternative therapies

The NFL has pointed out that marijuana's inclusion on the banned substances list is part of the collective bargaining agreement between the league and the players' union.

Both Morgan and Monroe are working with the NFL Players Association to form a pain management committee to look at all alternative pain therapies, including marijuana.

"Our guys are the ones feeling the pain. And our members have told us this is an important space to look at. That's why we're taking the initiative to do it," players' union spokesman George Atallah said.

the science on marijuana, potentially allowing the Players Association to argue for a temporary exemption for He believes that the committee -- which includes current and former players as well as medical experts -- can examinethe science on marijuana, potentially allowing the Players Association to argue for a temporary exemption for therapeutic use , as is currently done with the stimulants Ritalin and Adderall. However, Atallah reiterated that such a verdict hasn't been made and that it is up to the committee to determine where the science stands.

Monroe and Morgan hope that with the backing of Doctors for Cannabis Regulation, more current players will be willing to speak out.

The group is made up of physicians and others who believe that marijuana needs to be regulated and evaluated as a health issue, not a criminal one. Its board includes former US Surgeon General Joycelyn Elders.

"Players certainly are reluctant to voice their opinion on the issue because of the fear of being released, being blackballed," Monroe said. He points to himself as an example; Monroe believes his outspokenness was a factor in his release from the Baltimore Ravens

Sparked by 'Weed'

"The NFL sends the right message when they show they are willing to follow scientific evidence that suggests the safety and potential efficacy of cannabis use by NFL players," Doctors for Cannabis Regulation founder and President Dr. David Nathan said.

Monroe and Morgan point to CNN's documentary "Weed," reported by CNN's chief medical correspondent Dr. Sanjay Gupta , as instrumental in changing their understanding of the drug.

"The first 'Weed' documentary is what kind of put me on the whole medical aspect of everything and that really sparked my interest, especially looking at the neuroprotective properties of CBD," Morgan said.

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Morgan believes that marijuana is a crucial issue for the NFL when it says it's focused on the health and safety of its players.

"There are lot of things you deal while playing this game and when you leave this game. Just to have something to as an option, just for guys to understand what their options are and to have a plan about their health. To help them be proactive about it. I think it's worth any risk that can come from me talking out."