The nation's top doctor on Wednesday told CBS News that "marijuana can be helpful" for some medical conditions and symptoms.

"We have to see what the science tells us about the efficacy of marijuana," said US Surgeon General Vivek Murthy, who President Barack Obama nominated to the position in 2013. "We have some preliminary data showing that for certain medical conditions and symptoms, that marijuana can be helpful. I think that we have to use that data to drive policy-making. I'm very interested to see where that data takes us."

Some marijuana legalization and medical marijuana advocates quickly seized on Murthy's comments, pushing their agenda for the federal government to loosen restrictions on pot.

"Dr. Murthy's comments add to a growing consensus in the medical community that marijuana can help people suffering from painful conditions," said Tom Angell, head of the pro-legalization Marijuana Majority. "It's crazy that federal law still considers marijuana a schedule 1 drug, a category that's supposed to be reserved for substances with no medical value. In light of these comments from his top medical adviser, the president should direct the attorney general to immediately begin the process of rescheduling marijuana."

Marijuana is currently in the same category as heroin and an even higher restriction than cocaine.

Murthy said there's only "some preliminary data" showing marijuana has medical value, which falls far short of requirements for rescheduling the drug's classification. To find medical value for a controlled substance under the feds' scheduling system, a drug must have large-scale clinical trials to back it up — similar to what the Food and Drug Administration would expect from any other drug entering the market.

But the federal government's prohibition of marijuana is part of the reason large-scale clinical trials have been so hard to conduct. As a result of pot's schedule 1 status, the Drug Enforcement Administration limits the supply of marijuana for research. To obtain it for studies, researchers must get their studies approved by the Department of Health and Human Services, FDA, and DEA.

Given these restrictions, the American Academy of Pediatrics recently called on the federal government to reschedule marijuana to allow more research into its potential health effects for sick children.

In other words, changing marijuana's status as a schedule 1 drug is a bit of a catch-22. There needs to be a certain level of scientific research proving marijuana has medical value, but federal restrictions make that difficult.

Update: The US Department of Health and Human Services later released a statement attributed to Murthy:

Marijuana policy — and all public health policies — should be driven by science. I believe that marijuana should be subjected to the same, rigorous clinical trials and scientific scrutiny that the Food and Drug Administration (FDA) applies to all new medications. The Federal Government has and continues to fund research on possible health benefits of marijuana and its components. While clinical trials for certain components of marijuana appear promising for some medical conditions, neither the FDA nor the Institute of Medicine have found smoked marijuana to meet the standards for safe and effective medicine for any condition to date.

Watch: Ezra Klein's take on the subject

Hat tip to Tom Angell at Marijuana Majority for the tip.