GW Pharmaceuticals’ Epidiolex has become the first cannabinoid prescription medicine to be approved in the US, winning clearance to treat two rare forms of epilepsy.

In a historic move, the US Food and Drug Administration has given the green light for the drug’s use to treat seizures associated with Lennox-Gastaut Syndrome or Dravet Syndrome, two rare, severe and notoriously difficult-to-treat childhood-onset epilepsies.

“This approval is the culmination of GW’s many years of partnership with patients, their families, and physicians in the epilepsy community to develop a much needed, novel medicine,” noted the UK firm’s chief executive Justin Gover.

“These patients deserve and will soon have access to a cannabinoid medicine that has been thoroughly studied in clinical trials, manufactured to assure quality and consistency, and available by prescription under a physician’s care.”

Epidiolex contains cannabidiol (CBD), a chemical component of the cannabis sativa plant, more commonly known as marijuana. CBD does not cause intoxication or euphoria that comes from tetrahydrocannabinol (THC), the primary psychoactive component of the drug.

“This approval serves as a reminder that advancing sound development programs that properly evaluate active ingredients contained in marijuana can lead to important medical therapies. And, the FDA is committed to this kind of careful scientific research and drug development,” said FDA Commissioner Scott Gottlieb.

“Controlled clinical trials testing the safety and efficacy of a drug, along with careful review through the FDA’s drug approval process, is the most appropriate way to bring marijuana-derived treatments to patients. Because of the adequate and well-controlled clinical studies that supported this approval, prescribers can have confidence in the drug’s uniform strength and consistent delivery that support appropriate dosing needed for treating patients with these complex and serious epilepsy syndromes.”

More than 90 percent of patients with LGS or Dravet syndrome have multiple seizures per day, which puts them at constant risk for falls and injury.

In one clinical trial (published by The New England Journal of Medicine), Epidiolex reduced monthly drop seizures by 37.2 percent (10 mg/kg/day dose) and 41.9 percent (20 mg/kg/day), compared with a 17.2 percent reduction for placebo. In another (published by The Lancet) the reduction was 44 percent versus 22 for placebo.

In a study involving children with Dravet syndrome, five percent became seizure free while taking the drug compared to none in the placebo arm, and patients also had a significantly greater median reduction in convulsive seizures (39 percent) compared to placebo (13 percent).

“The difficult-to-control seizures that patients with Dravet syndrome and Lennox-Gastaut syndrome experience have a profound impact on these patients’ quality of life,” said Billy Dunn, director of the Division of Neurology Products in the FDA’s Center for Drug Evaluation and Research.

“In addition to another important treatment option for Lennox-Gastaut patients, this first-ever approval of a drug specifically for Dravet patients will provide a significant and needed improvement in the therapeutic approach to caring for people with this condition.”

The availability of Epidiolex is pending rescheduling, which is expected to occur within 90 days. GW’s subsidiary Greenwich Biosciences will market the drug in the US.