Nicole Gross was so desperate to find relief for her son's near-constant, debilitating seizures that she moved him from Naperville to Colorado so he could receive medical marijuana.

Weeks after Chase Gross, 8, started taking a marijuana oil extract through a dropper, his mother said she saw a dramatic decrease in the number of daily seizures he had, allowing him to make developmental leaps such as dressing himself and learning new sign language words, since his condition has left him unable to speak.

Gross became so convinced of pot's effectiveness in treating her son's severe epilepsy that she joined a growing number of parents and advocates lobbying Illinois to change its rules — not only to add epilepsy to the list of qualifying conditions but to make medical marijuana available to children, as Colorado and several other states do.

The drug's positive effects on Chase, his mother said, were "shocking."

Public opinion has been shifting in favor of medical marijuana: Twenty states have legalized it, and the vast majority allow children access to it. But its use, particularly among juveniles, remains controversial.

Marijuana is illegal under federal law, where it is classified as a dangerous substance with no medical value. While proponents cite largely anecdotal evidence as they lobby to expand the use of medicinal pot for a growing number of conditions, many physicians warn that there's not nearly enough research to demonstrate marijuana's effectiveness for treating sick adults — let alone children.

Dr. Kent Kelley, chief of pediatric neurology at NorthShore University HealthSystem's Evanston's hospital, treats several children who suffer from seizures and whose parents have asked him about marijuana as a last-resort option. He said he advises them to wait and to seek out clinical trials for their children.

"It's a hard thing to ask parents. On the other hand, it may not be as good as we think, so we want data to know how effective it is and what the risks are," Kelley said. He added that he would support the proposed change in the Illinois law but hopes more clinical research would take place first.

The American Academy of Pediatrics notes that while research on pot's potential therapeutic benefits is scarce, the drug's harmful effects on memory, motivation, judgment and motor control are well-known.

Dr. Sharon Levy, director of the Adolescent Substance Abuse Program at Boston Children's Hospital, said using state laws to sidestep federal medical regulations is bad public policy. She noted that marijuana abuse remains common among her patients and that use during adolescence is associated with drops in IQ and increased rates of schizophrenia and other psychiatric disorders.

While there may be rare special cases that warrant exceptions to the rule, Levy said, drugs derived from the marijuana plant, called cannabinoids, should go through the same rigorous testing and approval process as every other drug to show that they work safely. Otherwise, she said, children may be taking something that ends up doing more harm than good, particularly for conditions more common than extreme forms of epilepsy.

"Failing to develop cannabinoids as medication is a disservice to the kids who may benefit from them," she said. "The answer is better regulation, not less of it."

Marijuana advocates counter that federal regulation has stood in the way of the very research that is needed. The Drug Enforcement Administration classifies marijuana in the same category as it does heroin, as a Schedule I controlled substance with no accepted medical use and high potential for abuse. Yet of the 38,000 people who died from drug overdoses in the U.S. in 2010, according to the Centers for Disease Control and Prevention, 60 percent were related to prescription drugs, while reported deaths from marijuana are extremely rare.

Advocates argue that children with debilitating, sometimes fatal diseases don't have time to wait for the years it typically takes the Food and Drug Administration to approve a new medication. Many parents say they've already spent years giving their children prescription drugs that don't work or have horrible side effects and that they deserve access to other treatment options.

Before their struggle to help their son, Nicole and Randy Gross said they were the last people to support marijuana use.

Their feelings began to shift when they heard that other children with severe epilepsy were finding relief through marijuana. Chase is thought to have myoclonic-astatic epilepsy, also called Doose syndrome, and his parents say that before he started ingesting marijuana, he would have hundreds of short seizures each day.

The oily extract they administer their son is low in THC — the psychoactive component of marijuana that causes smokers to get "stoned" — and high in CBD, or cannabidiol, which has shown promising results in animal studies.

That strain of marijuana is known as Charlotte's Web, named after 5-year-old Charlotte Figi, who gained national attention last year when CNN reported that the drug had drastically reduced her severe seizures.

Though Charlotte previously could not walk, talk or feed herself, she is now doing all those things and riding a bike, according to her physician, Dr. Alan Shackelford, who also helped approve Chase for medical marijuana use.

But even advocates like Shackelford, who estimates he has seen about 30 children being treated successfully with medical marijuana, agree that the drug needs clinical trials to establish proper and standardized content and dosing. However, he said, time is of the essence.

About 200 kids are registered in Colorado to receive medical marijuana, according to the Colorado Department of Public Health and Environment. Children need approval from two doctors, not just one as for adults.

Dr. Larry Wolk, the department's director and chief medical officer, said it appears that most of the children approved to use medical pot have epilepsy, and the majority come from out of state. Yet children make up only a small fraction of medical marijuana patients, he said.

Wolk worries that the spotlight on children brings medical expectations that research has yet to support.

"It's possible that your child may not respond," Wolk said. "And it's also possible that even if your child does respond, you might be trading treating the seizure for creating a different kind of problem."