The Obama administration is planning to remove a major roadblock to marijuana research, officials said Wednesday, potentially spurring broad scientific study of a drug that is being used to treat dozens of diseases in states across the nation despite little rigorous evidence of its effectiveness.

The new policy is expected to sharply increase the supply of marijuana available to researchers.

And in taking this step, the Obama administration is further relaxing the nation’s stance on marijuana. President Obama has said he views it as no more dangerous than alcohol, and the Justice Department has not stood in the way of states that have legalized the drug.

For years, the University of Mississippi has been the only institution authorized to grow the drug for use in medical studies. This restriction has so limited the supply of marijuana federally approved for research purposes that scientists said it could often take years to obtain it and in some cases it was impossible to get. But soon the Drug Enforcement Administration will allow other universities to apply to grow marijuana, three government officials said.

While 25 states have approved the medical use of marijuana for a growing list of conditions, including Parkinson’s, Crohn’s disease, Tourette’s syndrome, Alzheimer’s, lupus and rheumatoid arthritis, the research to back up many of those treatments is thin. The new policy could begin to change that.