A new NOVA documentary, “The Cannabis Question,” delves into the actual effects of cannabis use, its role in the U.S. carceral system and what’s still unknown about the drug.

California was the first state to legalize marijuana for medical use a quarter of a century ago. Since then, more than 30 other states have followed suit, nearly 20 of which have also approved it for recreational use. But the federal government still classifies it as a Schedule I narcotic, alongside drugs like heroin. Because of that, tens of thousands of people — disproportionately people of color — are still behind bars for marijuana-related offenses, and scientists cannot conduct key medical research on it.

On Greater Boston, Jim Braude was joined by Sarah Holt, the director and producer of The Cannabis Question, and Kassandra Frederique, executive director of the Drug Policy Alliance, who is featured in the film.

“What we know is that our cannabis laws have consistently and historically been predicated on a desire to control groups of people,” Frederique said. Even the word “marijuana” has racial ties, she added.

NOVA: The Cannabis Question premieres Wednesday, September 29 at 9pm ET on GBH 2 and will be available to stream atpbs.org/nova via thePBS video app and on the NOVA PBS YouTube channel.

Join NOVA and experts from The Cannabis Question for a free virtual panel discussion and film highlights followed by a live Q&A. Thursday, October 7 at 6pm ET. Register to join.

WATCH: Director Sarah Holt and Kassandra Frederique, executive director of the Drug Policy Alliance