The company said the drug, Epidiolex, significantly reduced the monthly frequency of short-term seizures in people suffering from a rare form of epilepsy called Lennox-Gastaut syndrome (LGS).
In the trial, Epidiolex, when added as an adjunct to the patient’s existing treatment, achieved the primary endpoint of a significant reduction in the monthly frequency of drop seizures assessed over the entire 14-week treatment period compared with placebo (p=0.0135).
Epidiolex was generally well tolerated in this trial. 86% of Epidiolex patients experienced an adverse event compared with 69% of patients on placebo.
The positive results follow earlier success, in March this year, of a separate trial using Epidiolex for another epilepsy condition, dubbed Dravet syndrome.
GW Pharmaceuticals CEO Justin Gover said: "We believe that this result further demonstrates that Epidiolex offers the potential to be a new effective therapy within the field of treatment-resistant childhood-onset epilepsies.
"We now look forward to advancing Epidiolex towards the submission of an NDA with the FDA in the first half of 2017."
Apart from the first phase 3 study of Epidiolex in LGS, GW is undertaking a second phase 3 dose-ranging trial of the drug to treat LGS, which is fully enrolled at 225 patients.
The second trial has three treatment arms: Epidiolex 20mg/kg/day, 10mg/kg/day and placebo. GW expects to report top-line results from the study by the end of the third quarter of this year.