Former U.S. Attorney General Eric Holder expressed his belief in an interview with PBS's "Frontline" that the federal government should no longer classify marijuana as a Schedule I substance - a classification reserved for substances with a high potential for abuse and no currently accepted medical use.

"I certainly think it ought to be rescheduled. You know, we treat marijuana in the same way that we treat heroin now, and that clearly is not appropriate," he said. "So at a minimum, I think Congress needs to do that. Then I think we need to look at what happens in Colorado and what happens in Washington." 

The interview was conducted last year following Holder's departure from the administration but was released Tuesday along with the program's most recent documentary about the heroin crisis.

The effort to legalize marijuana on a state level has made major strides in recent years, with Colorado and Washington legalizing recreational marijuana and Alaska, Oregon and Washington, D.C., since following suit. Various other states have made similar efforts but in smaller steps, only going as far as decriminalizing possession of small amounts of marijuana.

This isn't the first time Holder has signaled support for changing the classification of marijuana, whose current status as a Schedule I substance makes it as dangerous as heroin or cocaine in the eyes of authorities. In 2014, he similarly questioned the logic in keeping marijuana in the same category as heroin which is confirmed to have both a high potential for abuse and no accepted medical use, according to the Huffington Post.

Despite speaking out about it and even going so far to say at a 2014 Congressional hearing that he would be more than glad to work with Congress to reclassify weed, little has come of it, and marijuana legalization advocates argue that Holder should have done more while he was still attorney general.

"It's nice to have Holder's support for this sensible policy change, but it would have been a lot better if he'd exercised the power to get marijuana rescheduling done while he was still in office," said Tom Angell, chairman of Marijuana Majority, a group that supports legalization.

It should be noted that even if marijuana is moved into a lower category, it wouldn't automatically make it legal under federal law. It would, however, open the door for scientific research into the drug which advocates say would lead to a stronger understanding of its medical benefits. Marijuana could then possibly be made legal nationwide once adequate research is complete.