Researchers have been studying the medical benefits of marijuana for years, but this month marks the first time the National Institute on Drug Abuse (NIDA), a research group funded by the US government, has acknowledged that cannabis extracts may help kill certain cancer cells and reduce the size of others.

NIDA quietly revised a page on its website titled, "DrugFacts: Is Marijuana Medicine?" this month to state that, "Evidence from one cell culture study suggests that purified extracts from whole-plant marijuana can slow the growth of cancer cells from one of the most serious types of brain tumors."

The update acknowledges research published last November in the journal Molecular Cancer Therapies by scientists from St. George's, University of London. The researchers found that THC, the main psychoactive ingredient in weed, and cannabidiol, an extract, caused "dramatic reductions" in the growth of glioma tumors in mice. Glioma accounts for 80 percent of malignant brain tumors in humans.

"We've shown that cannabinoids could play a role in treating one of the most aggressive cancers in adults," Dr. Wai Liu, lead author of the study, wrote in an op-ed for the Huffington Post last year. Previous studies have shown that THC may have anti-tumor benefits, but the wrong dose can potentially increase the size of tumors.

Marijuana's legal status and the stigma surrounding the plant have significantly hindered scientific research of its potential benefits. It is still considered a Schedule I controlled substance, alongside heroin, LSD, ecstasy, and other drugs the US government says have "no currently accepted medical use and a high potential for abuse."

Despite orders from Congress not to interfere in states where medical marijuana is legal, the Department of Justice has said it will continue to prosecute cases against individuals and organizations that violate federal law by selling the drug.

Malik Burnett, policy manager at the Drug Policy Alliance, told VICE News that NIDA's recent admission about the efficacy of medical marijuana, coupled with the DOJ's vow to continue cracking down on the drug, is tantamount to "major hypocrisy" by the federal government.

"We have the Justice Department continuing to threaten patients with arrest and prosecution in spite of the fact that Congress has voted to prevent the Justice Department from interfering with states that have passed medical marijuana laws," Burnett said. "These are all just parts of the major hypocrisy within the federal government when it comes to the issue of marijuana."

The US Food and Drug Administration (FDA) has not approved medical marijuana to treat any illness, but the agency has approved medications that contain cannabinoid chemicals in the form of a pill.

NIDA's website notes that, "continued research may lead to more medications," but the institute has been blamed for stymieing medical marijuana research by running a monopoly on pot grown for research purposes.

NIDA manages a contract with the University of Mississippi, which grows and supplies "research-grade marijuana," though some of the few people able to obtain government's weed have described it as low-grade "schwag" that is brown and full of seeds and stems. While NIDA does not directly control who receives marijuana for research, there is a laborious three-step approval process that applicants must fulfill in order to obtain the drug.

Twenty-three states and the District of Columbia have now enacted medical marijuana laws. Illinois expanded its medical marijuana program Monday, issuing around 2,000 licenses to patients.

Responding to the DOJ's vow to continue medical marijuana prosecutions, Bill Piper, director of national affairs for the Drug Policy Alliance, urged US lawmakers to take up the cause in a statement released April 2.

"Congress should respond to the Justice Department's insubordination by changing federal law," Piper said. "Patients and the people who provide them with their medicine will never be safe until states are free to set their own marijuana policy without federal interference."