The US House of Representatives passed a bill Wednesday that would broaden researchers' ability to study marijuana and its effects, a move hailed by cannabis advocates. 

The bill, passed in a bipartisan voice vote, allows authorized researchers access to parts of cannabis plants grown under state programs. 

The use of marijuana for medical purposes is legal in 36 of the 50 states plus Washington, and for recreational use in 15 states plus the capital.

But until now, only the University of Mississippi was federally licensed to grow and clinically research the drug.  

The plants that were available for study at the university, however, were of "poor quality" and failed "to accurately reflect the varieties of marijuana commercially available in the United States," according to US pro-cannabis organization NORML. 

"The reality that most high-schoolers have easier access to cannabis than do our nation's top scientists is the height of absurdity and an indictment of the current system," said NORML deputy director Paul Armentano. 

Bill co-sponsor Earl Blumenauer, a Democratic lawmaker from Oregon, welcomed the law's passage in the lower house of Congress.

"It's illegal everywhere in America to drive under the influence of alcohol, cannabis or any other substance. But we do not have a good test for impairment because we can't study it," he said.

He pointed out that four million Americans have received permission to use cannabis for medical purposes and that "many more likely self-medicate" with it. 

Maryland Republican Andy Harris was the bill's other co-sponsor -- he opposes the legalization of marijuana while Blumenauer supports it. 

But "we agree 100 percent that we need to do this research," Harris said. 

The bill must next be approved by the Senate to take effect.  

The Democratic-controlled House last week also passed a bill that would remove cannabis from the federal list of dangerous drugs, a historic step towards federal decriminalization of the substance. It stands little chance however in the Senate, which is controlled by Republicans.