In January, President Barack Obama said reclassifying marijuana and making it legal in any way "is a job for Congress."
"It's not something by ourselves that we start changing," Obama said in an interview with CNN.
In February, 18 members of the U.S. House of Representatives shot back in a letter to the president, telling Obama he should use his executive power to make the change on his own.
Caught in the middle are the more than 1 million Americans who use marijuana for their physical and psychological ailments.
They don't like the situation, saying they face daily uncertainty about whether they'll be able to get the drug they need or whether they'll be arrested for possessing it.
"Without cannabis, I can't get out of bed," said Steph Sherer, the founder and executive director of a group called Americans for Safe Access.
On Monday, the medical pot users took their complaints to Congress.
Concluding a three-day conference in Washington, the group organized 200 medical-marijuana advocates from 37 states _ a collection of patients, doctors, scientists, lawyers and others _ for its second annual lobbying day on Capitol Hill, lining up more than 300 meetings with legislative offices.
Pot backers say Congress needs to get involved to resolve a growing conflict between state and federal laws.
They expressed hope that change could be in the offing after Attorney General Eric Holder told a House subcommittee Friday that the Obama administration is ready to tackle the issue.
While stressing that "ultimately Congress would have to change the law," Holder said, "I think our administration would be willing to work with Congress if such a proposal were made." He's expected to field questions on the topic again Tuesday when he appears before the House Judiciary Committee for a hearing on oversight of the Justice Department.
While Congress classifies marijuana as a Schedule 1 substance with no medical value, 20 states have passed laws allowing medical pot since California became the first in 1996, and Florida is expected to vote on the issue in November. Two states, Washington and Colorado, went farther in 2012, passing laws that allow all adults who are 21 and over to smoke pot for recreational purposes.
But medical marijuana users say the state laws can easily be ignored by federal authorities, who have the discretion and authority to override them as they see fit. Medical marijuana advocates say a change in federal law would eliminate any confusion and ensure that patients and their suppliers are operating legally.
They complained that the Obama administration has spent more than $300 million to prosecute medical marijuana cases since 2009, $100 million more than was spent during the entire eight years of George W. Bush's presidency.
"We're really just relying on Congress to actually reschedule it at the federal level, because until that happens, all of this on the state level is almost meaningless," said Kari Boiter, a patient from Washington state who's involved with Americans for Safe Access.
She said that was particularly the case for people who were going to prison for using marijuana and for family members who were "left to deal with the fallout."
"This is very real right now: The federal government in Washington state, where it is legal, is prosecuting at least three people that I know of," Boiter said.
Critics say it would be a mistake to reclassify marijuana, calling it a dangerous drug that's highly addictive. In states such as Kentucky, where lawmakers killed a medical marijuana bill earlier this year, some lawmakers said the drug had not undergone enough testing.
Sherer, who founded Americans for Safe Access in 2002, began using marijuana when she was 23 for chronic neck pain. After a severe injury affected her neck's mobility and caused spasms, she began using painkillers, muscle relaxants and high doses of ibuprofen, which led to kidney problems. She said she used marijuana because she couldn't take ibuprofen now.
Addressing a large group of legislative staff members over lunch on Monday, Sherer said medical marijuana patients shouldn't have to worry about getting safe supplies of their drug or such things as "prosecutorial discretion."
"What this means is that if a U.S. attorney feels like prosecuting someone, he or she will," Sherer said.
She said decision-makers in Washington should stop pointing fingers "at who should take the first step" in rescheduling marijuana. And she said the question facing Congress was not whether the drug was a medicine.
"Cannabis is a medicine. It has been used for thousands of years," Sherer said. "What we are asking your bosses to do is to change outdated laws so they reflect the experience of their constituents."
Medical marijuana backers say their top priority is to pass a bill introduced by Democratic Rep. Earl Blumenauer of Oregon.
Among other things, it would put Congress on record as recognizing the medical value of marijuana and prevent the federal government from interfering with any state-approved medical pot programs.
But it would not offer federal protections to anyone smoking pot without authorization from a doctor, including recreational users in Washington state and Colorado.
By Rob Hotakainen
McClatchy Washington Bureau