The U.S. Department of Justice said Native American tribes can grow and sell marijuana on their lands in a December 11 statement, while President Obama signed a federal spending bill into law on Tuesday which includes a provision protecting medical marijuana.

Since the spending bill had to pass both houses of Congress before landing on the president's desk, the inclusion of this provision shows changing attitudes among both Democrats and Republicans, according to Michael Collins, policy manager for the Drug Policy Alliance.

"It's a real game-changer," Collins said. "For the first time ever, both parties in Congress recognize that states should be setting their own medical marijuana policies. It's a recognition of the validity of medical marijuana as a treatment, and it's an effort to end federal prohibition of medical marijuana. It gives us great hope for ending federal prohibition of marijuana for all uses."

The provision discourages federal drug agents from raiding state-legalized medical marijuana operations. It also represents the culmination of years of work, according to Morgan Fox, communications manager for the Marijuana Policy Project.

"We’ve been trying to get this bill passed since 2003, and the fact that it finally did is indicative of steadily changing attitudes in Congress and nationally among voters," Fox said.

That's not to say these operations are entirely in the clear -- marijuana is still illegal under federal law, and federal agents have other tools with which to make things difficult on growers and sellers.

"Feds effectively use the threat of civil forfeiture to get private land owners to evict and/or not lease to cannabis-related businesses," said Allen St. Pierre, executive director for the National Organization for the Reform of Marijuana Laws. "A great number of these medical cannabis businesses are cash-only businesses, because federal banking regulations still deter banks from doing business with these new cannabis-related businesses, and money laundering opens up prosecution opportunities for feds."

"While the Obama Administration currently tolerates marijuana legalization in states with 'strong and effective regulatory and enforcement systems,'  the next administration may have a different approach to marijuana," Kilmer said.

Meanwhile, the announcement that Native American tribes can grow and sell the drug on their lands -- provided they follow the same federal guidelines as have been laid out for states pursuing legalization -- came as a surprise to many advocates.

"No one at NORML or other drug policy reform groups knows the impetus for this sudden change in cannabis policy directed at Native American tribes," St. Pierre said. "Speculation is that a number of tribes in states with medical cannabis and tax-and-regulate access have been seeking clarity from the Department of Justice regarding what if any commerce can they engage in re cannabis?"

In addition to being an economic benefit, marijuana could provide a health benefit for tribes in a position to grow and sell, Fox said.

"By making marijuana legal for adults on their territory, Native American groups have an opportunity to increase public health and safety," he said. "In addition, tribes could create jobs and tax revenue while taking advantage of tourism. Many groups are in a position to do this long before the states within which their territories reside, all while giving their members a safer legal alternative to alcohol."

Even after these strides toward legalization, advocates have big plans for the year to come.

"While not expected to move in Republican-controlled Congress and Senate, there will be upwards of 17 re-entered or new legislative bills introduced in 2015 dealing with cannabis, ranging from ending the federal cannabis prohibition, to re-scheduling for medical/research only, industrial hemp, sentencing reform, banking regulations, creation of national commission to end cannabis prohibition, etc.," St. Pierre said. "Again, none are expected to move in the Congress. Reformers will be delighted to even be given hearings by the majority."

Editor's note: The policy only discourages federal agencies from raiding medical marijuana dispensaries; it does not explicitly prohibit such action.