Former NBA Commissioner David Stern, who tightened up the league’s policy on marijuana during his tenure from 1984 until 2014, has reversed his opinion on the subject. In an interview with former NBA star Al Harrington, who now works in the cannabis industry, Stern said marijuana “probably should be removed from the banned substance list.”

Stern’s declaration came at the end of a long conversation with Harrington, who looked taken aback after Stern’s statement.

“That’s huge,” said Harrington, who began using cannabinoids, or CBD — which does not contain the psychoactive substance THC that’s commonly associated with marijuana highs — to treat an ongoing knee injury.

Harrington is making a documentary for Uninterrupted.

Stern said given the decades in which he ran the NBA, he believes he made the right choice to tighten up the league’s rules on the drug.

“Some of our players came to us and said some of these guys, they’re high coming into the game,” Stern recalled. “At that time, people generally accepted that marijuana was a gateway drug and if you start smoking you’re liable to go on to bigger and better stuff.”

Stern agreed with Harrington, however, and said times have changed.

“It’s a completely different perception [of marijuana],” Stern said, crediting a 2013 CNN documentary on the subject hosted by Sanjay Gupta with helping to change his mind. “I think there’s universal agreement that marijuana for medical purposes should be completely legal.”

Stern continued: “If you [Harrington] tell me that it worked for you and it worked for other people, then we should find a way to get that defined and made official and then proceed to educate team docs. I think all of the leagues are appropriately focused on player training . . . player rehabilitation in the case of injury, player nutrition [and] . . . this should be a part of that conversation. Could you imagine if we could create a situation where every superstar was able to play one additional year?”

Like Harrington, Stern eschews the wide use of painkillers, specifically those that are addictive such as oxycodone and other opioids. Unlike Harrington, however, Stern has not tried medical marijuana himself. He expressed excitement, though, when Harrington said he brought Stern a few gifts.

Harrington got into the marijuana industry after retiring from the NBA because of complications with his knees. Since then, he has been a proponent of the cannabis products, even turning his grandmother onto marijuana to treat glaucoma and other ailments.

“At that point, I just started looking at this as just medicine,” Harrington said in the documentary. “It’s not just about rolling a joint. It’s bigger than that.”

Harrington isn’t the only former athlete who has become a marijuana evangelist.

Several former NFL players have credited the drug with saving their lives, including ex-Baltimore Ravens lineman Eugene Monroe, who was released in June 2016, just three weeks after becoming the first active NFL player to call on the league to allow medical marijuana.

“This pain is never going away. My body is damaged,” Monroe, 30, told The Post’s Rick Maese in May. “I have to manage it somehow. Managing it with pills was slowly killing me. Now I’m able to function and be extremely efficient by figuring out how to use different formulations of cannabis.”

Like in the NBA, marijuana — used for both recreational and medical purposes — remains on the NFL’s prohibited list. NFL Commissioner Roger Goodell, however, has said he is willing to evaluate the potential medical uses cannabis might offer players.

NBA Commissioner Adam Silver has also said he’s “open” to discussing the issue of medical marijuana, but for now, the league is retaining its present policy and will keep it on the banned list.

“While Commissioner Silver has said that we are interested in better understanding the safety and efficacy of medical marijuana, our position remains unchanged regarding the use by current NBA players of marijuana for recreational purposes,”—NBA Executive Vice President Mike Bass said in an emailed statement.

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