The placebo controlled study involved 171 patients with Lennox-Gastaut syndrome. Epidiolex reduced the number of seizures in a month by 44 percent, compared with those taking a placebo medication that reduced seizures by 22 percent.

In March, another Phase 3 trial of Epidiolex also showed positive results in children with Dravet syndrome, another form of childhood epilepsy. GW is also conducting a Phase 3 trial of Epidiolex in Tuberous Sclerosis Complex and expects to initiate a Phase 3 trial of Epidiolex in infantile spasms in the fourth quarter of this year.

If approved by the Food and Drug Administration, the drug would be the first cannabis derived drug to win approval for the treatment of childhood epilepsy. Epidiolex has both Orphan Drug Designation and Fast Track Designation from the FDA. GW plans to formally file for FDA approval later this year.

GW is already marketing a marijuana-based oral spray called Sativex that is being sold in Europe, Canada and Mexico to treat muscle tightness and contractions caused by multiple sclerosis. Canada also allows Sativex to be used for the treatment of neuropathic pain and advanced cancer pain.

Sativex is not currently approved for use in the U.S. for any condition. It is estimated that over 400,000 cancer patients in the U.S. suffer from pain that is not well controlled by opioid pain medications. However, two recent Phase 3 studies found that Sativex worked no better than a placebo in treating cancer pain.