And the first skeptic he faced was his wife, Nureya.
When Monroe first shared his self-appointed mission in December, Nureya was confused. She had understood marijuana as illegal and dangerous since childhood, and ever since they met at the University of Virginia, she'd known her husband as a health-shake-chugging, gluten-free, dairy-free, pescatarian athlete who didn't use marijuana.
"That conversation," Nureya said, "was a lot of me rolling my eyes."
But once Monroe described peer-reviewed studies and explained the benefits, she learned the difference between cannabis compounds. Her initial skepticism dissipated. "It definitely has allowed me to say, 'Wow, this is something that can help people,' " Nureya said.
Monroe has moved to trying to win over the NFL, volunteering for a role nobody assigned him, a crusade born of his own principle. In May, he became the first active player to publicly call for the NFL and NFL Players Association to remove cannabis from their list of banned substances and permit medical marijuana to treat chronic pain inherent to professional football, which he believes -- and some research attests -- will reduce the league's glaring reliance on addictive opioid pills. He wants the NFL to further study the potential for cannabis to prevent or treat concussions. He donated $80,000 to University of Pennsylvania and Johns Hopkins researchers to further study marijuana use in professional football players.
Monroe's outlook derives from both firsthand experience with concussions and pain-killing pills and watching how former teammates have suffered. Monroe, 29, is at the peak of his playing career, seven seasons behind him and two years into a five-year, $37.5 million contract. He realizes he plays in a league where players can be suspended entire seasons for testing positive for marijuana or tumble in the draft if their marijuana use is made public. His head coach, John Harbaugh, has said pointedly Monroe does not speak for the Ravens organization.
"To this point, I understand why no one but me as an active player has said anything about it," Monroe said. "It's a banned substance in our league. Speaking about it can honestly ruin someone's career if the wrong team gets wind of it, and has adverse opinions on it. But my health is more important than the opinion of someone who could be my employer now or my future employer. ...
"There's enough anecdotal evidence already to say, 'Hey listen, we know it's not toxic. We know it's safer than what we're already doing.' "
An NFL spokesman had little to say about Monroe's campaign, referring to comments Commissioner Roger Goodell made in February before the Super Bowl. "We always review our drug policy," Goodell said then. "That is something that our medical professionals do on a regular basis. We have had discussions with them in the past about that, not recently."
Quietly, though, the NFL has shown interest in Monroe's campaign.
Jeff Miller, the league's senior vice president for player health and safety, and neurological surgeon Russell Lonser, a member of the league's head, neck and spine committee, spoke Thursday afternoon on a call with the researchers Monroe has funded to learn more about their study. The league officials, while not endorsing Monroe's stance, requested the talk and were eager to hear more about it.
"They are interested in learning more about the potential for cannabinoids to help current and former players, as is evidenced by them taking the call, and also expressed a desire to learn more," said Marcel Bonn-Miller, an assistant professor at the University of Pennsylvania school of medicine. "They are definitely showing genuine curiosity, and they are definitely not throwing up roadblocks."
Monroe's advocacy comes as America's views on marijuana continue to shift and the country's opioid crisis grows starker. Twenty-four states plus the District of Columbia have legalized medical marijuana, with more likely by year's end. Four states plus the District have legalized it in full. Meantime, overdoses related to prescription pain medication caused 19,000 deaths in 2014, the latest figures released by the American Society of Addiction Medicine. The number rises to nearly 40,000 when heroin overdoses are factored in, and prescription pain killers can lead to heroin use.
"In my mind, there's no comparison if we just started from scratch in the year 2016 and looked newly at which class of drugs worked better to treat pain and side-effect profile up to and including death, in the case of opioids," said Daniel Clauw, a University of Michigan professor who has performed studies comparing opioids and cannabis. "You put the two next to each other, and there really is no debate which is more effective to treat pan. You would go the cannabinoid route instead of the opiate route."
Wednesday afternoon at a local juice bar, Monroe outlined his stance. He is a skilled and disciplined messenger, amiable yet forceful, eloquent but not conversational. His response to an interviewer's first question lasted more than five minutes. He does not present himself as a radical, but rather as an emissary of common-sense science that has been dismissed owing to outdated stigma. When it was mentioned that cannabis has yet to be conclusively proven to aid in concussions, Monroe casually interrupted, "The U.S. Department of Health has a patent -- 6630507 -- defining it has neuroprotective capabilities in the event of traumatic injury to the brain."
Earlier this year, as Monroe gathered information and prepared to go public, Nureya posed a question to him. "What do you want to come out of this?" she asked.
"I want to break down the doors," Monroe replied. "And if I can get a huge organization like the NFL to acknowledge this is something we can do to help people, if the NFL can say we're looking into marijuana research for our players, the stigma is going to leave."
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Growing up in Plainfield, N.J., Monroe said, he saw drugs destroy lives in his community and "I would get as far away from it as humanly possible." He said he still does not use cannabis out of fear of failing an NFL drug test. "I can't afford to take the hit," he said.
Monroe's interest in the topic began in 2013, when he watched the CNN documentary "Weed" by physician Sanjay Gupta. It featured children who curbed debilitating seizures by using medical marijuana. Monroe grew curious about the application of medical marijuana to treat NFL players' pain.
What he learned shaped his current pitch: The NFL must reform its policies on marijuana, because the status quo leaves players vulnerable. Whereas opioids can lead to addiction, organ damage and overdose, cannabis is not addictive and doesn't cause death. Cannabis can treat chronic pain as effectively as opioids, and in cases where opioids are necessary, such as after surgery, using cannabis reduces the necessary dosage, thereby reducing the risk of addiction.
He learned the differences between the at least 113 cannabinoids marijuana contains. THC is the psychoactive compound, the reason recreational users seek it. But cannabidiol, or CBD, provides analgesic and anti-inflammatory properties. CBD can be extracted into oil and administered in pill form that doesn't render a high. Monroe came to believe the majority of what he'd been taught about marijuana was a lie, the harm it caused overblown and the potential benefits ignored.
The issue came into personal focus for Monroe last season. He suffered a concussion the first week of the season in Denver. Sitting in the visiting locker room, he had no idea how he had gotten there. Flying to California that night, team trainers gave him Tylenol, "which did nothing," he said. The next day, he couldn't open blinds in his room because the light hurt too much, and he could barely walk down the hallway to see a doctor because he was so dizzy.
Following the season, he underwent shoulder surgery and took pain killers. They made him queasy, so he stopped. He felt he needed a different option, and he thought about all the other players facing similar pain, dependent on addictive pain killers.
Before he started publicly touting his view, Monroe spoke with NFL Players Association representatives, but he found them less responsive than he hoped. He didn't reach out to any one with the Ravens.
"And quite frankly, I didn't need to," Monroe said. "This is a matter that can't wait."
The NFLPA did not respond to multiple messages seeking comment. The NFL did not indicate any change from its previous stance, which is that it will listen to medical advisers and has found no reason to change its view.
Monroe has seen some interest from league personnel. During a passing conversation, he said, a Ravens team doctor inquired about what he'd learned regarding cannabis.
"He had seen some of the statements I've made, and he was interested in becoming more educated," Monroe said. "He understands country-wide, we have a problem with how we prescribe pills to manage pain. And this can be a healthier option."
In public comments, Ravens owner Steve Bisciotti largely has supported Monroe.
"Obviously Eugene is a pretty stand-up, professional guy," Bisciotti said at the NFL owners meetings in March. "To have an opinion about something like that is partial to being a leader if it matters to him. We're not the ones taking that physical abuse. We're not talking about a kid that's been suspended three times coming out and saying that. I respect Eugene a lot, and I think all he asked for is more studying on the subject."
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Some experts say cannabis could provide a solution to the NFL's thorniest problem. Past research suggests, but has yet to prove, cannabis may play a role in preventing and treating concussions. CBD has been shown to have neuroprotective properties. Animal research indicated CBD could protect neurons and mitigate effects from concussions by protecting the brain nerves and tissue by attaching to receptors in the brain.
Lester Grinspoon, a professor emeritus at Harvard and one of the first medical marijuana researchers, said players should not only be allowed to use cannabis, but encouraged to take it before they play.
"We have no guarantee this is going to work," Grinspoon said. "But if you can take anything away, evidence shows it is neuroprotective. I would have each individual take a capsule an hour or two before they play or practice. It's better than nothing."
Monroe's donation was a boon for a field that faces hurdles. Grants are hard to come by because marijuana remains a Schedule I substance and illegal in so much of the country. There is a relatively thin canon, because for years the vast majority of studies focused on the harm, not the potential value, of marijuana.
The researchers plan two observational studies, Bonn-Miller said, one on former players one on current players. Along with providing 80 percent of the funding for the studies, Monroe provided insight about the design and helped create a network of current players willing to participate.
"We wouldn't be where we are with him," Bonn-Miller said. "The findings from this can inform a lot of groups. It's directly driven by NFL players right now, but it has widespread implications, that there are a lot of groups that are going to benefit, not just NFL players."
Monroe could have waited until after his playing career to speak out. He believes his message would have fallen on deaf ears had it not come from an active player.
"My life is literally at risk here," Monroe said. "Like I said, I've got children, man, and I worry for my future. I've already had a few concussions. It's time for us to grow up, to move past 'Reefer Madness,' to understand this as real medicine."