A Montana dad is claiming that medical marijuana helped cure his 2-year-old son's massive brain tumor.

Mike Hyde, 27, said he slipped a little cannabis oil into his toddler Cash's feeding tube after the boy stopped eating for 40 days. Chemo treatments were making him too sick to eat.

"Not only was it helpful, it was a godsend," Hyde told ABC News.

Hyde had used medicinal marijuana to treat his own attention deficit disorder, and he got Cash a card after doctors found a malignant brain tumor on his optic never in 2010.

After doctors started an aggressive chemo treatment, the tot lost his appetite and threw up 10 times a day, his dad said. The little boy also suffered septic shock, a stroke and internal hemorrhaging.

"When he started the chemo, he was so sick," Hyde said. "For the first six weeks, he was blind...It's the nastiest thing to see someone you love go through this."

After doctors inserted a feeding tube into Cash's stomach, Hyde said he boiled up a little weed with olive oil and poured tiny doses into it, hoping to ease the boy's nausea and get him eating again.

Hyde never told doctors, because medical marijuana is illegal in Utah, where the boy was being treated. It is legal in Montana, where the family lives.

Miraculously, the boy recovered last fall.

"In two weeks he was weaned off all the nausea drugs, and he was eating again and sitting up in and laughing," Hyde said.

Doctors said the dad's impromptu pot treatment was surprising, but risky.

"I think that the fact that he didn't have the rapport and ability to be honest with the doctor is very troubling," Dr. Linda Granowetter, a pediatrics professor at NYU, told ABC.

"It's awfully hard to gauge if a child would have a bad reaction," she added. Granowetter said the idea that pot can cure cancer is "ludicrous."

Medical marijuana is legal in 16 states and commonly used to treat nausea associated with cancer treatments, as well as glaucoma and other stomach illnesses.

It has not been tested on children.

Hyde said his doctors called the recovery "miraculous," but warned him that there was a 50-to-80% chance that the cancer would come back.

Hyde and his wife set up a foundation to help children with cancer, and said doctors at the hospital told him he was "one of the best dads."

"I was told he was going to die, but I knew he hadn't stopped the fight," he said.