After years of denial, the Drug Enforcement Administration finally admitted Wednesday that "heroin is clearly more dangerous than marijuana."

Chuck Rosenberg, the new head of the DEA, made the remark to reporters to clarify on a less definitive statement made just a week ago, when he said that marijuana is "probably not" as dangerous as heroin, The Huffington Post reported.

"If you want me to say that marijuana's not dangerous, I'm not going to say that because I think it is," Rosenberg said last week, according to U.S. News. "Do I think it's as dangerous as heroin? Probably not. I'm not an expert."

The somewhat vague answer sparked criticism from the media and hearkened back to controversial statements from the DEA's former chief, Michele Leonhart. While testifying before the House Judiciary Subcommittee on Crime, Terrorism, and Homeland Security in 2012, Leonhart infamously refused to acknowledge that marijuana was not as dangerous as other drugs like heroin and crack. Leonhart resigned earlier this year following revelations that DEA agents partook in sex parties with prostitutes in Colombia, which were financed and facilitated by drug cartels.

Rosenberg expanded on his clarification on Wednesday, saying that he believes cannabis is still "harmful and dangerous," just not as dangerous as heroin.

His comments represent a significant shift in the DEA's position on marijuana and bring the agency into alignment with the science that has long held that marijuana is one of the least dangerous and addictive recreational drugs.

A 2010 study published in the British peer-reviewed journal Lancet ranking 20 drugs based on harm factors found that alcohol posed the most harm to both users and others, and heroin posed the second greatest danger. Marijuana was ranked as the eighth most harmful, while psychedelic mushrooms were ranked the least harmful. Another more recent study published in 2015 in Scientific Reports compared the lethality of the recreational use of 10 common drugs, including marijuana, alcohol, heroin and tobacco. It found that marijuana has the lowest risk of mortality and is safer than the rest in the study.

Marijuana is, however, still classified by the DEA as a Schedule 1 drug under the Controlled Substances Act, alongside heroin and mushrooms. This classification is reserved for drugs with the highest potential of abuse and no medical value.

Recreational marijuana has been legalized in four states and the District of Columbia, and 23 states have legalized the plant for medicinal purposes.

Marijuana advocates offered praise and poked fun at Rosenberg's remarks.

"It's sort of remarkable that a DEA chief simply saying heroin is more dangerous than marijuana could actually make news," Ethan Nadelmann, executive director of the Drug Policy Alliance, one of the world's largest organizations fighting for the reform of marijuana laws, told HuffPo. "I guess that's a reflection of how out of touch his predecessor was -- that she couldn't bring herself to simply state the obvious."

Dan Riffle, director of federal policies for the Marijuana Policy Project, said he is happy the DEA is acknowledging "what any rational person has known for years."

"In other news, the sky is blue," he joked.