The decision by the Drug Enforcement Administration, reported by news outlets late Wednesday, means marijuana will remain classified as a Schedule 1 drug. A formal announcement is expected Thursday.
Many scientists have been calling for the federal government to reschedule the drug, which they said would open the door to more medical research into marijuana and its potential effects, both beneficial and harmful.
To conduct research with Schedule 1 drugs, scientists have to gain DEA approval and often upgrade the security protocols in their labs, expensive and time-consuming hurdles.
Scientists have argued that thorough research is all the more important with medical marijuana available in 25 states and Washington, and a small number of states starting to legalize recreational marijuana as well.
Researchers also need the highest level of permission to run clinical trials of marijuana and drugs derived from it, and to study constituents of marijuana, even if they are free of the components that make people high.
A component of marijuana called cannabidiol has shown promise in treating people with epilepsy, and other researchers want to study marijuana as a potential therapy for post-traumatic stress disorder and for pain.
Proponents of keeping marijuana classified at Schedule 1 say the extra steps are a reasonable precaution for researchers to take given that it's a substance shown to have some negative impact on developing brains and given that some people become dependent on it.
They argue regulations have not completely stalled research with marijuana. Companies have sponsored clinical trials of drug candidates made from marijuana, and according to the DEA, the number of scientists registered to study the substance rose from 161 in April 2014 to 244 in March 2016