But the science is far from settled on whether marijuana, or components of it, can effectively treat seizures, and the parents cautioned that what made sense for them may not for other families.

Dr. Igor Grant, director of the Center for Medicinal Cannabis Research at the University of California San Diego, said there is some data to suggest cannabis can have anti-epileptic effects, “but not terribly systematic data.”

He said that the Brills’ experience, as a single anecdote, is not proof that cannabis works as a treatment, but added that it should not be dismissed.

“I don’t mean we should rush out and give marijuana to everyone who has epilepsy,” he said, “but I think that there are probably epilepsies that would benefit from an alternative treatment if they’re not controlled by our usual treatments.”

Ms. Brill said that she had been upfront with David’s doctors about the marijuana use, and that they hadn’t protested. But then she told the boy’s therapist on April 19, and hours later the police were at their door.

The police drug-tested all three of them: Mr. Brill and David tested positive for marijuana, Ms. Brill tested negative. The parents admitted to the police that they had given their child marijuana, and the officers demanded they stop, Ms. Brill said.

“We complied, and within 14 hours of complying we were rushing our son to the hospital,” she said. “And it was one of the most horrific seizures I’ve ever seen.”