US Surgeon General Dr Vivek Murthy declares using marijuana for medicinal purposes "can be helpful". Getty

The US Surgeon General has endorsed the medicinal qualities of marijuana saying the drug "can be helpful" in treating certain conditions and symptoms.

Speaking on CBS News, Dr Vivek Murthy, said: "My position is that we have to see what the science tells us about the efficacy of marijuana, before hinting that marijuana laws may need to be reformed."

He cited "some preliminary data for some medical conditions and symptoms" before declaring that "marijuana can be helpful."

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

His comments highlight the federal government's apparent inconsistent approach in dealing with marijuana for medicinal purposes.

In 2013, the US Department of Justice announced it would not challenge state marijuana laws governing medical usage. But recently federal lawyers were in court trying to close a medical cannabis operation in Oakland, California.

The drug has been legalised for medical marijuana usage in 23 states including Washington DC and made legal for recreational purposes in Colorado and Washington State.

At the federal level, marijuana remains a Schedule I drug – the same classification as heroin - and is not deemed to have "no currently accepted medical uses".