(CNN) January 19 is when more than 1.2 million patients legally using medical marijuana will be watching Congress with great concern.

That's when the Rohrabacher-Blumenauer amendment will expire. The amendment essentially stops the Justice Department from spending any federal dollars on prosecuting cannabis-related activities if those activities are allowed under state medical marijuana laws.

The amendment was extended in the spending bill in December , but unless Congress slips it into another federal spending bill and can pass it before the law expires, the legislative action that US Attorney General Jeff Sessions took Thursday may have a real impact on people who sell or buy medical marijuana.

Sessions rescinded three memos that relate to federal law enforcement of marijuana laws, the last of which, popularly known as the Cole memo, was 2013 guidance that essentially told the government to back off federal prosecutions of people operating within state marijuana laws.

and to other federal efforts to shut down licensed medical dispensaries. Raids of medical marijuana establishments continued after the memos went out, but the amendment put an end to those raidsand to other federal efforts to shut down licensed medical dispensaries.

In rescinding the three memos Thursday, Sessions advised prosecutors to "follow the well-established principles that govern all federal prosecutions." He viewed "previous nationwide guidance specific to marijuana enforcement (as) unnecessary."

Sessions' memo didn't specifically mention prosecuting anyone involved with medical marijuana, but if the Rohrabacher-Blumenauer amendment expires, nothing will stop them, experts said. And Sessions sent a letter to congressional leaders in May arguing against the continued restriction of Justice Department funds for prosecutions, suggesting that such a policy was "unwise," "particularly in the midst of an historic drug epidemic." That letter concluded that marijuana "has significant negative health effects."

Congress has maintained that marijuana is a dangerous drug. The DEA has kept it as a Schedule I controlled substance, putting it in the same category as LSD and heroin, with "no current acceptable medical use." Medical marijuana and CBD oil, which comes from hemp but on the molecular level is the same as CBD from marijuana, are both in this category.

"I knew the risk. I knew we were breaking the federal law when I started giving it to my daughter Charlotte, but the risk was worth it because it was a matter of life or death," said Paige Figi of Colorado, whose daughter has a rare form of epilepsy that gives her hundreds of seizures a week that at one point kept her from being able to walk, talk or eat. Charlotte started using CBD oil when she was 5, and it transformed her life.

"She's 11 now, and she's doing great and running around," Figi said. "This is usually fatal, and she is doing awesome, and for years and years, this is all she has had to take."

to that affect is under consideration in the Senate. Figi said she wasn't surprised by the Sessions move -- "nothing surprises me anymore" -- but she hopes it may motivate Congress to enact legislation that would at least deschedule CBD, meaning people could use it without breaking federal law. A billto that affectis under consideration in the Senate.

Though the scientific research on marijuana is still considered limited , users say it helps with chronic pain and sleep problems, among other health benefits. Some studies have shown that it helps with post-traumatic stress disorder

Breiter, who describes himself as conservative, said he would like to remind Sessions that "there is much more consistency in the scientific literature of findings about the detrimental effects of alcohol, which is legal within a strong regulatory framework." He thinks there needs to be more research on the topic and a more logical legal framework applied to the drug.

Some states are pushing back against Sessions' latest guidance, including Colorado and Washington, where medical and recreational marijuana are allowed. Both have said they will continue to defend their laws in court.

In Michigan, which only began accepting applications for medical marijuana licenses in December, it's business as usual despite the Sessions memo. Michigan's Department of Licensing and Regulatory Affairs said it will "continue to move forward in accepting and processing applications for state operating licenses," according to a statement from David Harns , the department's public information officer.

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for help in figuring out what their next steps will be. Medical marijuana dispensaries have been calling Americans for Safe Access , a nonprofit working to ensure safe and legal access to marijuana for therapeutic uses and research,for help in figuring out what their next steps will be.

Steph Sherer, the organization's executive director, said she had nearly deleted the program it offered to guide dispensaries about raids as the Obama administration relaxed its rules. Now, she's glad she didn't, and she said dispensaries should be prepared for anything.

"I'm very nervous," she said. The Drug Enforcement Administration "is run out of Washington, and while they are supposed to serve states' attorneys general, the DEA doesn't need their permission to do anything in those districts."

Polls have shown that the greater majority of Americans do favor medical marijuana. "If we can stay focused, maybe the silver lining is, Congress remembers how important this amendment is and that we need Congress to come up with a permanent solution," Sherer said.