GW Pharmaceuticals' cannabinoid Epidiolex continues to impress in late-stage clinical trials, with a Phase III study involving patients with Lennox-Gastaut syndrome - a rare and severe form of childhood-onset epilepsy - the latest to hit its targets.

Shares in the group shot up more than 20 percent as it trial data emerged showing that, when Epidiolex was added as an adjunct to patients' current treatment, there was a significant reduction in the monthly frequency of drop seizures assessed over the entire 14-week treatment period versus placebo.

Drop seizures were defined as atonic, tonic and tonic-clonic seizures involving the entire body, trunk or head that led or could have led to a fall, injury, slumping in a chair or hitting the patient's head on a surface. During the treatment period, patients taking Epidiolex achieved a median reduction in monthly drop seizures of 44 percent compared with a reduction of 22 percent in patients receiving placebo.

Overall, the drug was generally well tolerated, the firm noted, with 86 percent of all Epidiolex patients experiencing an adverse event compared with 69 percent in the placebo arm, the most common of which were diarrhoea, somnolence, decreased appetite, fever and vomiting.

Of those patients on Epidiolex who reported an adverse event, 78 percent reported it to be mild or moderate, and of the twenty patients who experienced a serious adverse event in the group, nine were deemed treatment related.

"Lennox-Gastaut syndrome is such a difficult form of epilepsy to treat. Additional safe and effective treatments are desperately needed for patients who continue to struggle with uncontrolled seizures," said Christina SanInocencio, Executive Director of the Lennox-Gastaut Syndrome Foundation.

"We are thrilled with these positive results, which offer much needed hope and promise to those living with this debilitating condition."

GW said it is expecting to submit a New Drug Application for Epidiolex in LGS with US regulators in the first half of 2017.

The news follows positive results from a pivotal Phase III trial of Epidiolex for the treatment of Dravet syndrome earlier this year, as well as the start of a late-stage trial testing the drug as an adjunctive therapy for the treatment of seizures associated with the rare genetic disorder Tuberous Sclerosis Complex, of which epilepsy is a key symptom.