Drug Enforcement Administration acting Chief Chuck Rosenberg reiterated an Obama-era stance Thursday that "marijuana is not medicine."

"If it turns out that there is something in smoked marijuana that helps people, that's awesome," he said, speaking at the Cleveland Clinic in Ohio. "I will be the last person to stand in the way of that. ... But let's run it through the Food and Drug Administration process, and let's stick to the science on it."

Marijuana is classified as a Schedule I drug under the Controlled Substances Act, alongside drugs like heroin and LSD, while other substances like oxycodone and methamphetamine are classified as Schedule II drugs, which are regulated differently. Despite repeated attempts by advocates requesting that marijuana be moved to Schedule II, the DEA has pointed to the FDA's guidance that says it does not have medical value.

Rosenberg noted that the DEA takes recommendations about how to classify the drug from the FDA. He pointed out that marijuana studies have been ongoing and acknowledged some studies show it may have medical benefits for children with epilepsy.

Former Surgeon General Vivek Murthy, who was speaking alongside Rosenberg at the event, said that the country should be researching medical marijuana.

"Should we be reducing the administrative and other barriers to researching that in the government? 100 percent," he said. "But what we should not do is make policies based on guesswork. When we do that, what we do is put people at risk."

He also appeared to show some concern around state laws regarding recreational marijuana, saying that it is addictive, which can be harmful to a developing brain that is vulnerable to developing substance abuse and addiction.

State legislators, he said, have gotten "caught up in momentum" and passed policies on recreational marijuana that aren't always supported by science.

"When you develop a substance use disorder at a young age, it actually increases the likelihood of you developing an addiction to other substances," he said. "So in that sense addiction to marijuana or any substance, including nicotine, during adolescence and young adulthood when the brain is developing is very concerning."

"I worry that we have gotten away from allowing science to drive our policy when it comes to marijuana," he added.