Former Baltimore Ravens offensive tackle Eugene Monroe thinks the NFL needs to reevaluate its policy on medical marijuana. AP Photo/Lynne Sladky, File

Former Baltimore Ravens offensive tackle Eugene Monroe didn't give up football last year because he got too old, or because he couldn't hack it in one of the most lucrative positions in football anymore — he left because of repeated head injuries.

And now, a year into his retirement, the 30-year-old has taken up a new cause: Convincing the NFL that players should be able to use medical marijuana.

"I'm only 29 and I still have the physical ability to play at a very high level," Monroe wrote in a piece for Player's Tribune announcing his retirement in May 2016. "But I am thinking of my family first right now — and my health and my future."

In the piece, Monroe discussed how his 18-year love affair with the game left him foggy-headed and "terrified" of life-long brain injuries like chronic traumatic encephalopathy (CTE). Team doctors would prescribe him opioid-based painkillers and anti-inflammatory pills, which left him reeling from side effects.

"I just thought that for longevity purposes that wasn't ideal, and I needed an alternative way to manage pain and inflammation," Monroe told Business Insider. "Cannabis was a glaring option."

A year later, he's devoted himself to cannabis activism, working with partners like Green Flower Media to educate others about how cannabis can be a much healthier alternative to opioids.

It all started in the locker room

Offensive tackle is one of the most demanding positions in football, fraught with big collisions and the injuries that follow. When Monroe was a player, team doctors prescribed him pills after games for each injury he sustained. That's where the trouble started.

"Then I'd need more pills on top of those to deal with the side effects," Monroe said, detailing the disorientation, lethargy, headaches, and gastrointestinal issues he suffered from the opioid-based painkillers and anti-inflammatory drugs he was prescribed.

After announcing his retirement, Monroe began researching alternatives to the pills he was prescribed. That research led him down a year-long education into the world of cannabis, which has been "awesome," as he puts it.

Monroe said that he has found cannabis to be "way more effective" than the litany of opioids he was prescribed while playing for the Ravens, and he suffers none of the side effects he was accustomed too.

Monroe's experience is backed up by science. A January study from the National Academies of Sciences, Engineering, and Medicine (NASEM) found "substantial evidence" that the main compounds in cannabis — THC and CBD — are effective at treating and relieving chronic pain.

Just like opioid painkillers bond to natural opioid receptors; cannabinoids like THC and CBD bond to the body’s natural cannabinoid receptors. Doctors think the cannabinoid system may play a crucial role in pain management, though the study notes that more research is needed to suss out the connection.

There's research showing that medical cannabis can alleviate pain, but doctors are still hesitant. REUTERS/Mario Anzuoni/File Photo

Further studies have shown promising results that CBD could have a "neuroprotective," effect and may reduce the risk of developing CTE. The disease is a major issue in professional sports — a 2015 study from Boston University's CTE Center found that 96% of the deceased NFL athletes they examined showed signs of CTE.

Monroe donated $80,000 of his personal money to researchers at Johns Hopkins and the University of Pennsylvania to study medical marijuana for brain injury treatment.

Doctors are still hesitant to recommend cannabis outright — pain management is a complicated — and there's still a ton of uncertainty around cannabis products. Cannabis's status as a Schedule 1 drug makes it difficult for doctors to obtain quality samples for research.

Despite Monroe and a number of other NFL players, including Nate Jackson and Ricky Williams, insisting that the NFL reevaluate its policy towards medical marijuana, NFL leadership has so far declined to do so.

Not so fast, says the NFL

Marijuana use has been a hot topic in the NFL in recent years. Perhaps the most high-profile case is that of Cleveland Browns wide receiver Josh Gordon, who was suspended for the entire 2015 season for smoking marijuana.

Though Gordon's 2015 suspension wasn't the first time he ran afoul of the NFL's substance abuse policies, he was arrested for driving under the influence in 2014, he recently completed a stint in rehab for his marijuana use. The NFL, however, denied the Browns' petition to have him reinstated.

He's not the only player who's been hounded by the NFL for marijuana consumption. Chicago Bears offensive lineman Kyle Long criticized the NFL's position banning cannabis — while allowing alcohol and prescribing opioids — on Twitter earlier this month. Just days later, he was selected to take a drug test by the league.

Roger Goodell, the NFL's commissioner, has not been positive about cannabis use, calling it "addictive" on an ESPN radio show in April.

"Is it something that can be negative to the health of our players? Listen, you’re ingesting smoke, so that’s not usually a very positive thing that people would say," Goodell said.

Monroe called Goodell's statements "disheartening," and countered that no credible people are recommending smoking cannabis — there are other, much healthier and more precise methods of consumption.

"It's time for the NFL to look at this from a different lens," Monroe said. "It's not 1995 — we're in a different place now."

Monroe says he prefers vaping — which heats up the cannabis flower to a point where it releases active compounds but doesn't actually combust — as well as topical ointments containing THC that he can rub on painful joints and muscles.

Companies in Colorado, where cannabis is legal under state law, are also rapidly developing pills, and sub-lingual oils that players can take which offer a much more effective dose than, say, smoking a joint.

The NFL is widely popular — but many of its players are suffering. Joe Robbins/Getty Images

What the NFL can do, according to Monroe, is commit some of the $100 million it is using to research player head injuries and safety to examine cannabis.

"If this is a business decision then you're giving athletes problems that are decreasing their performance," Monroe said. "Those side effects have a very direct effect on a player's ability to practice, participate in the game."

Monroe added that in his view, there's "no question" cannabis is safer than the opioid-based drugs that NFL doctors prescribe. "There's no need for opioid drugs" in states where cannabis is legal, Monroe said.

Keeping up with the Joneses

There have been some promising movements from influential people in the NFL in recent weeks. Dallas Cowboy's owner Jerry Jones told a meeting of team owners in April that the NFL should drop its prohibition on cannabis use.

Cannabis, however, is a collective bargaining issue, meaning that NFL players must make a concession in exchange for changes to the NFL's policy, according to NBC Sports.

Monroe called it "atrocious" for the NFL to "try to bargain something like this."

"The decision to simply no longer punish players for using marijuana — I don't think that needs to be negotiated," Monroe said. "That's something that can be added to the current language of the [Collective Bargaining Agreement]."

Carl Francis, a spokesman for NFL player's association told Business Insider that they will "continue to explore this area," and "work with our pain management committee to learn more," about cannabis.

George Atallah, another NFLPA spokesman, told NBC's Pro Football Talk earlier this month that it's "incumbent upon all of us to take the hard look and see how we can help players."

"I think it’s incumbent on the league office to, and pardon my pun, keep up with the Joneses," referring to the Cowboy's Jerry Jones, and his son, Cowboys VP Stephen Jones, who has also called for re-thinking the NFL's cannabis policy.

It comes down to money. Players likely aren't going to give up higher salaries in exchange for the NFL relaxing its marijuana policies. The NFL, if it's truly concerned with player safety, should lead the charge by diverting a portion of its massive budget to medical cannabis research, Monroe says.

To Monroe, the NFL's double standard with cannabis is glaring.

"It's safer than every intoxicating beer that the NFL advertises and sells in all of its stadiums," Monroe said.

The NFL, a largely conservative, highly public, $13 billion organization based on 2016 revenue, will take some time to updates its cannabis policy to shift with the times. But it's worth fighting for, Monroe said.

"Roger Goodell needs to put his big boy pants on and look at this and understand that he can do something very profound for his players," Monroe said.