GW Pharmaceuticals (GWPH) - Get Report announced positive results Monday from a second, pivotal clinical trial involving children with a severe form of epilepsy treated with its experimental marijuana-based drug.

Shares of GW Pharma are up 16% to $96.52 in Monday premarket trading.

In the phase III study, treatment with the GW Pharma drug epidiolex resulted in a 44% reduction in monthly drop seizures compared to a 22% reduction for placebo. The difference was statistically significant.

The study enrolled 171 children (average age: 15) with Lennox-Gastaut Syndrome. Despite taking an average of three medicines to reduce seizures, the patients were still having a median of 74 drop seizures per month. The study added Epidiolex or placebo on top of the patients' other anti-seizure medicines.

Diarrhea, sleepiness, decreased appetite, fever and vomiting were the most common adverse events reported in the study, although a majority were mild to moderate. Twenty patients on epidiolex reported a severe adverse event, nine of which were deemed to be related to the drug. Twelve patients discontinued epidiolex during the study compared to one placebo patient. One epidiolex patient died during the study but the cause was found to be unrelated to the drug, GW Pharma said.

Monday's positive results support results from a phase III study of epidiolex in Dravet Syndrome patients announced last March. In that previous study, treatment with epidiolex resulted in a 39% reduction in monthly convulsive seizures compared to a 13% reduction for placebo.

GW Pharma has already announced plans to seek regulatory approval for epidiolex in the first half of 2017.

Epidiolex is a pharmaceutical-grade formulation of pure cannabidiol (CBD) found in marijuana.

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