WEDNESDAY, May 24, 2017 (HealthDay News) -- A landmark clinical trial has shown that a compound in marijuana can ease life-threatening seizures in children with a rare and devastating form of epilepsy.

Cannabidiol -- a non-intoxicating chemical -- reduced seizure frequency by 39 percent in patients with Dravet Syndrome, researchers report.

This is the first randomized, controlled trial to show that cannabidiol (CBD) can help control seizures in some people with epilepsy, said study author Dr. Orrin Devinsky. He is director of the Comprehensive Epilepsy Center at NYU Langone Medical Center in New York City.

"It's a big landmark in the scientific study of cannabis, and it's a major landmark in epilepsy care," Devinsky said. "After four millennia of using cannabis to treat epilepsy, we now have for the first time scientifically rigorously obtained data that this specific compound works in this specific form of epilepsy."

Brandy Fureman, vice president of research and new therapies for the Epilepsy Foundation, agreed that the new trial provides "gold standard" evidence of cannabidiol's effectiveness.

"We now have strong evidence that CBD [cannabidiol] can be helpful for some people with Dravet Syndrome," Fureman said. "This trial provides important information for doctors and families who are trying to decide if CBD should be tried in their child's particular case, how it can be administered safely, and what side effects to watch out for."

The clinical trial relied on a liquid formulation of cannabidiol called Epidiolex, which was developed by British company GW Pharmaceuticals.

Epidiolex has not been approved by the U.S. Food and Drug Administration. GW Pharmaceuticals -- which paid for the clinical trial -- expects to file for FDA approval of the drug this year.

In the trial, Devinsky and his colleagues recruited 120 children and teenagers with Dravet Syndrome, which generally starts causing severe seizures within the first year of life. The seizures often are prolonged and repetitive; 1 in 5 children with Dravet Syndrome do not live to see age 20, Devinsky said.

The patients, ranging in age from 2 to 18, were randomly assigned to receive every day either 20 milligrams of liquid Epidiolex or a placebo, on top of their usual medication. The study took place across 23 sites in the United States and Europe, and lasted 14 weeks.