"It's always a tricky issue prescribing really a medication of any kind to developing organisms because they may be more sensitive to the effects, specifically if the prescription drug has an effect on the brain," Grant said.
He said there have been basic laboratory studies that suggest pot slows cancer cells' ability to change, but those studies are only theoretical. They include no clinical data and or animal data.
The American Academy of Pediatrics opposes treating children with medical marijuana.
"The issue is that marijuana isn't a medicine," Dr. Sharon Levy, of the AAP, told the Oregonian.
Seger said she has several concerns about a 7-year-old taking pills filled with cannabis oil because there is little research on its long-term effects on children. Cannabis could have potentially negative effects on cognitive development in children since it affects cognitive ability in adults.
But Purchase said she wasn't afraid to give her daughter the pills last summer. She was a little nervous about determining the right dose. She and her fiancé, Brandon Krenzler, who helped raise Mykayla since she was 3 years old, started MyKayla with .07-gram doses.
"It took a while to get her adjusted to it," Purchase said. "She acted more funny when she first started taking it and after a while gained tolerance. Now, when she takes it, you can't even tell. She's very normal."
Purchase said she knew she'd done the right thing the day Mykayla missed a dose of her cannabis oil pills and her 17-month old sister walked into a room holding string cheese. The smell made Mykayla so sick that she threw up on the spot.
"She actually asked for her dose," Purchase said, adding that she's less perky without it. "She doesn't use pain pills or nausea pills. She has not even lost a single pound since her diagnosis."
Dr. Michel Dubois, who works in NYU Langone's Pain Management Center, said using cannabis is still controversial because of its side effects and addictive qualities.
"This is a new ethical problem because you've got a medication, which is known to have psychoactive affects, approved by the parents and given to a child," he said, adding that the child doesn't have much choice in the matter. (Psychoactive drugs disrupt communication in the brain and alter normal awareness, behavior and mood, according to the National Institute on Drug Abuse.)
Dubois said it would be better to give a child other drugs for nausea because the cannabis oil likely contains at least 50 or 60 different chemicals with unknown long-term health effects. If Mykayla's life expectancy is limited, her risk of toxicity will also be limited. However, if she is expected to make a full recovery, Dubois said there is a worry that the cannabis will add health problems later on.
He said the cannabis shouldn't be used for more than a month or two.
Although Mykayla's doctors told Purchase she was in remission on Aug. 6 when her blood cell counts returned to normal, Mykayla will undergo two and a half or three more years of chemotherapy so that she can one day be officially cured, Purchase said. That could mean years of more medical marijuana.