A cannabis-based drug was effective at treating children with a very rare form of epilepsy, the drug manufacturing company GW Pharmaceuticals announced Monday.

GW said the results from the Phase III stage of the study found that Epidiolex, a drug that contains cannabinoids, the active ingredients from marijuana, helped reduced the number of epileptic seizures in children with Dravet syndrome. 

The study involved 120 patients diagnosed with Dravet Syndrome. The participants had a median age of 10, and 36 of them were younger than six. Sixty-one patients took 20 mg of Epidiolex per day while the remaining 59 took a placebo drug on top of their current anti-epileptic drug (AED) regimen. The median baseline for the number of convulsive seizures was 13 per month.

By the end of the 14-week treatment, the researchers found that the monthly frequency of convulsive seizures for children taking Epidiolex was reduced by a median of 39 percent. The rate of decline measured in the placebo group was 13 percent. The difference between the two groups was considered to be statistically significant.

"This shows that cannabinoids can produce compelling and clinical important data and represent a highly promising new class of medications, hopefully in a range of conditions," Chief Executive Officer Justin Gover said.

Gover added that GW plans to request a meeting with the U.S. Food and Drug Administration (FDA) to discuss the process of getting Epidiolex approved and on the market. There are currently no approved treatments for this rare type of epilepsy in the United States.

"The results of this Epidiolex pivotal trial are important and exciting as they represent the first placebo-controlled evidence to support the safety and efficacy of pharmaceutical cannabidiol in children with Dravet syndrome, one of the most severe and difficult-to-treat types of epilepsy," said Orrin Devinsk from the New York University Langone Medical Center's Comprehensive Epilepsy Center. "These data demonstrate that Epidiolex delivers clinically important reductions in seizure frequency together with an acceptable safety and tolerability profile, providing the epilepsy community with the prospect of an appropriately standardized and tested pharmaceutical formulation of cannabidiol being made available by prescription in the future."

More results from the final stages of the Phase III study trials are expected later on this year. In one of those trials, the researchers are testing Epidiolex's effects on another rare form of epilepsy called Lennon-Gastaut syndrome. Another Epidiolex trial for a third type of epilepsy, tuberous sclerosis complex, is scheduled to start soon. The researchers will also be carrying out a second Phase III trial that plans to enroll 150 patients with Dravet Syndrome.

"It clearly provides us with an excellent basis to be confident about the outcome of the additional trials because this trial has shown that the previous open-label data was very predictive," Gover said.

Epidiolex was considered to be well tolerated. The most common side effects included reduced appetite, vomiting, diarrhea, fatigue, fever, drowsiness/sleepiness, upper respiratory tract infections and convulsion.