Medical marijuana has passed a tipping point in the United States, with some form of cannabis now legal in 25 states and Washington, DC.

But despite growing mainstream acceptance, the federal government still maintains that weed has "no currently accepted medical use."

Since 1970, federal authorities have listed marijuana as a Schedule I controlled substance, a tightly regulated classification reserved for the most "dangerous" drugs, including heroin.

Cocaine and meth are both in the less restrictive Schedule II category with most opioid painkillers, while other medically useful substances like steroids, Xanax, and cough syrup are spread across Schedules III-V.

But weed's Schedule I status may change — and soon.

On April 4, the heads of the Drug Enforcement Administration (DEA) and Food and Drug Administration (FDA) sent a letter to members of Congress that said a decision would likely be made on rescheduling "in the first half of 2016." With just three days left in June, that deadline is fast approaching.

Removing marijuana from the Schedule I category would have huge ramifications, potentially impacting the future of state-level marijuana laws and making it significantly easier for scientists to study the drug's benefits and harms.

Asked recently for an update, DEA spokesperson Rusty Payne told VICE News, "We don't have a timeline on the decision."

The attorney general and DEA have the final say on rescheduling, but the FDA offered its official stance on the issue at least eight months ago, according to the agencies' joint letter to members Congress, which said the DEA received the FDA's input sometime prior to September 30, 2015. Neither agency, however, is currently willing to reveal what the FDA thinks ought to happen.

The FDA also rejected a public records request from VICE News for documents related to the matter, citing the DEA's pending decision and a provision that allows federal agencies to withhold certain "intra-agency memoranda." The broad and oft-used exemption the FDA cited in its decision is commonly known as the "withhold it because you can clause." It previously allowed such records to be kept secret forever, but Congress just passed a reform that forces disclosure within 25 years.

Katherine Uhl, a FOIA official with the Department of Health and Human Services, told VICE News the FDA has received "10 to 20" similar requests. She said the FDA typically releases records that receive that much public interest, but in this case the agency is holding back while the DEA mulls how to proceed.

This Oct. 14, 2015, file photo, shows the Food & Drug Administration campus in Silver Spring, Md. AP Photo/Andrew Harnik, File

"People tend to think if FDA were to say something now, that's what the DEA is going to to do, but that might not happen," Uhl said. "We don't put stuff out when it's still preliminary. We don't want people to jump the gun and get the wrong impression. They [the DEA] might not agree with what the FDA told them to do."

Technically, Uhl is right: The DEA is not legally required to follow the FDA's advice, and has significant discretion over whether marijuana remains Schedule I. But the FDA's recommendation carries a lot of weight, especially when it comes to deciding whether or not marijuana has a "currently accepted medical use."

Payne, the DEA spokesperson, said that if the FDA decides a drug is not considered medicine, the DEA is "bound" to keep it in the Schedule I category. But if the FDA calls for moving a drug into a less restrictive category, the DEA is free to ignore that suggestion, though that almost never happens.

"If they recommend a Schedule II-V, we then have the discretion whether or not to reschedule," Payne said. "Aside from a long debate whether to reschedule hydrocodone, we've never gone against the FDA recommendation." In that case, he noted, the two sides ultimately agreed that hydrocodone, an opioid used in painkillers, should be in the Schedule II category.

The DEA and FDA have reviewed marijuana's scheduling status several times before, most recently in 2011. In explaining the decision to keep weed in the same category as heroin, then–DEA chief Michele Leonhart noted the lack of "adequate safety studies."

"At this time, the known risks of marijuana use have not been shown to be outweighed by specific benefits in well-controlled clinical trials that scientifically evaluate safety and efficacy," she said, adding that "long-term, regular use of marijuana can lead to physical dependence and withdrawal... as well as psychic addiction or dependence."

Leonhart's explanation hinges on a catch-22: Marijuana's Schedule I status forces researchers to hack through a jungle of red tape in order to study it. Even so, there's now mounting evidence that marijuana is both safe and effective in treating some medical conditions.

The American Medical Association and the American Academy of Pediatrics have bothcalled on the DEA to reclassify the drug, and there's also growing movement among activists to "deschedule" marijuana by removing it from the list of controlled substances entirely, meaning it would be treated like alcohol or tobacco.

Public opinion is also overwhelmingly in favor of changing marijuana's status, with 61 percent of Americans now supporting legalization and a whopping 81 percent favoring legalization strictly for medical use.

A recent analysis by John Hudak, deputy director of the Center for Effective Public Management at the Brookings Institute, concluded that it's unlikely rescheduling would force states to alter their existing medical and recreational marijuana markets. But it would, he said, be an "important step in harmonizing federal and state policy," that would "eventually help millions of patients and families" by facilitating further medical research.

Hudak told VICE News that it's "completely normal" for the FDA to withhold its recommendation from the public until the DEA makes a decision, but he cautioned that even if the FDA rules that marijuana has medical value, the DEA can argue that the risk of abuse is too high to remove it from Schedule I.

"It allows the DEA to have a way out if they disagree with the FDA," he said. "[The DEA] can say 'Thank you for telling us there's medical value here,' but [then] say, 'There's the issue of abuse, so we're going to reject your recommendation and go with the status quo.'"

He also seemed to think the FDA's recommendation would be released only if it turns out the two agencies agree on how to proceed. Otherwise, he speculated, the records might remain locked away indefinitely.

"If the FDA recommends rescheduling and the DEA says no," Hudak said, "that will never see the light of day — unless someone leaks it."

Payne rejected that claim, saying "everything will be made public in the Federal Register" once the DEA's decision is final.