The United States' top doctor said that medical marijuana can help some patients in comments on Wednesday that may boost pressure on the Justice Department to redesignate the drug under federal law.

In an interview on "CBS This Morning," U.S. Surgeon General Vivek Murthy said the medical effectiveness of marijuana had to be shown scientifically and much more information about it was coming.

"We have some preliminary data showing that for certain medical conditions and symptoms, marijuana can be helpful," said Murthy, who became surgeon general in December.

"I think we have to use that data to drive policymaking, and I’m very interested to see where that data takes us."

The Justice Department designates marijuana as a Schedule I controlled substance, a category for drugs that have no accepted medical value and have a high potential for abuse.

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Twenty-three states and the District of Columbia have legalized medical marijuana, according to the Drug Policy Alliance advocacy group.

Florida also allows a narrow use of medical marijuana. Two states, Washington and Colorado, have legalized marijuana for recreational use.

Tom Angell, chairman of Marijuana Majority, another advocacy group, said in a statement that Murthy's remarks mean that President Barack Obama should direct Attorney General Eric Holder to begin changing how the department categorizes marijuana.

"Dr. Murthy's comments add to a growing consensus in the medical community that marijuana can help people suffering from painful conditions," Angell said.

The Justice Department had no immediate response to Murthy's comments.