PROVIDENCE, R.I. - When Debra Nievera went before lawmakers to ask them to legalize medical marijuana, she envisioned a program that would let her safely acquire the drug to alleviate the painful symptoms of the intestinal disorder Crohn's disease and other ailments.

She will probably be disappointed.

Rhode Island this month became the 11th state to allow sick people to use marijuana as medicine. But federal law still bans the drug, and none of the states where medical use is allowed have found a way for patients to legally, conveniently and safely acquire the drug.

In some states, passage of a medical marijuana law has had little effect because there is no system set up to get pot to sick people. In others, dozens of people have been arrested for providing medicinal marijuana.

People in those states warn the road ahead in Rhode Island will likely not be as smooth as patients like Nievera hoped.

The federal government classifies marijuana as a controlled substance with no medical value. Doctors cannot legally prescribe it, and pharmacies cannot stock it.

Most states have tried to strike a middle ground, registering patients with diseases such as cancer and AIDS and letting them or people designated as their caregivers grow small amounts of marijuana for the patients' use.

Max Schlueter, who oversees the state office in Vermont where patients who want to use marijuana must register, said it's not that simple - many patients there have been left wondering where they're going to get the drug.

"They're just not going to try to score some dope on the street," Schlueter said.

Just 23 people have applied to the state's medical marijuana program since it was set up two years ago, and he said he believes that's partly because of the supply issue.

California took a different approach when it passed the first medical marijuana law in 1996. Patients there don't have to register with the state and can pay caregivers to grow pot for them. Cities such as Oakland and Santa Cruz have designated official growers.

The result is a boom in marijuana clubs that grow hundreds of plants for thousands of patients. A few years ago, the state had 30 dispensaries, said Hilary McQuie, spokeswoman for Americans for Safe Access, a medical marijuana advocacy group. Today, there are 175.

McQuie estimated that 120,000 Californians use medical marijuana because it is relatively easy to get. Oregon, the state with the most patients registered, has about 12,000 in its program.

Rhode Island is unlikely to develop a California-like system. Its law limits caregivers to growing pot for five people.

In all states, those who grow medicinal marijuana risk getting arrested by federal authorities. The most famous supplier arrested may be Ed Rosenthal, an author of several books on how to grow marijuana. He served one day in prison in 2003 for growing pot for patients in Oakland, Calif.

Rosenthal, who had more than 100 plants when he was arrested and is appealing his conviction, said it's not realistic for states to expect patients - many of whom are disabled or weakened by illness - to grow their own pot.

"If we talked about any other medicine, people would get outraged," Rosenthal said. "What if you said to a diabetic, 'Well, you have to register with the state, you can only have so much at one time, you have to buy it on the black market.'"

In Colorado, there have been about a dozen high-profile medical marijuana arrests a year by state and federal authorities since the state legalized medical marijuana in 2000, said Sean McAllister, founder of Sensible Colorado, which advocates for changes in state drug policy.

Diane Brackett, spokeswoman for the Drug Enforcement Agency's field office in New England, said the agency does not target medical marijuana patients but focuses on large-scale growers and dealers. So, while growers like Rosenthal attract the DEA's attention, medical marijuana advocates point out that plenty of people buy pot every day without being arrested.

"I could pick up a phone and get some if I needed some," said Rhonda O'Donnell, 43, of Warwick, who suffers from multiple sclerosis and pushed to have medical marijuana legalized in Rhode Island. "I already know people, and I think most people do."

While some medical groups, including the Rhode Island Medical Society, support medical marijuana laws, other advocates and physicians say they are concerned about the quality of medicinal marijuana when it's bought on the street. Also, unlike prescription drugs, which are tightly regulated, dosage is hard to control when the patient is smoking a plant.

"If you're not growing it yourself, you don't know what you are getting," said Schlueter, who runs Vermont's registry. "And I'm not talking about marijuana that's been adulterated with rat poison, but just has it been stored properly? Is it dusty? Is it moldy? These people have compromised immune systems."

That's one thing that worries Nievera, 52, of Coventry, who said she is unwilling to buy pot on the street.

"You don't know what the quality is, if you are wasting your money," she said.

Tom Riley, a spokesman for the federal Office of National Drug Control Policy, which lobbied Rhode Island's legislators to vote against medical marijuana, said the lack of regulation is one of his agency's main objections.

"That's not how we do medicine in this country," he said. "What you really have created here is one track for all other medicines, and another for marijuana."