The network's chief medical correspondent tells THR there is a persistent stigma attached to the drug and says that he plans more reporting on the topic.

Dr. Sanjay Gupta's views on medical marijuana are evolving. In a candid admission, CNN's chief medical correspondent wrote an op-ed this week, "Why I Changed My Mind on Weed," explaining that he reevaluated his stance on the use of marijuana in certain medical treatments.

Timed three days before his CNN-financed feature doc, Weed, debuts Sunday night, he made headlines for his reversal of opinion. Appearing on the network's Piers Morgan Tonight, both Gupta and Piers Morgan discussed the issue, each noting that they had tried marijuana a long time ago and didn't particularly care for it.

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In the lead up to the premiere of Weed, Gupta spent a year working on the special -- and he has plenty of additional reporting that didn't make the final cut. "I think we’re going to be doing a lot more reporting on this," he told The Hollywood Reporter by phone. "When you spend a year on something, you have far more material than you can put into an hour."

The doc wades into the potential benefits and risks of the drug, with the CNN correspondent traveling to Colorado as well as locations in Israel where medical marijuana research is being conducted.

"Dating back to the times of Reefer Madness back in the mid-'30s, there’s been a persistent stigma attached to it," Gupta said. "And it’s been something that’s really stuck in the United States, more so than in many other countries."

In Gupta's op-ed, he points out that the majority of research done on medical marijuana specifically investigates the potential harms of the drug and not the benefits. The correspondent explains to THR that bureaucratic roadblocks have hindered researchers who set out to look at the positive effects of marijuana users.

"You have a few bureaucratic hurdles to get through, the last of which is an organization [the National Institute on Drug Abuse] whose core mission is to study abuse. It starts to make it a very difficult thing to study benefit in this country," Gupta said.

Weed continues the network's strategy of airing more documentaries and programming outside of its politics and news headlines roots. In June, the first episode of CNN's Inside Man, starring Morgan Spurlock as host, featured the Super Size Me filmmaker working at a medical marijuana dispensary.

Gupta's documentary approaches the topic from a neuroscientist's point of view. "Let me make something clear: When we talk about medicinal marijuana, the idea that people are using it to simply get high, that’s not true," the correspondent explained.

Weed airs Sunday night at 8 p.m. EST on CNN, with an additional showing Monday.

Twitter: @Erik_Hayden