Updated from 7:58 am EDT.

A new drug based on marijuana developed by GW Pharmaceuticals (GWPH) - Get Report reduced the frequency of seizures in children with a severe epileptic disorder in a late-stage clinical trial, the company said Monday.

Shares of GW Pharma rose 115% to $82.90 in Monday trading.

GW Pharma says it plans to discuss the positive findings from the phase III study with the U.S. Food and Drug Administration regarding a possible approval filing.

In the phase III study, treatment with the GW Pharma drug, Epidiolex, resulted in a 39% reduction in monthly convulsive seizures compared to a 13% reduction for placebo. The difference was statistically significant.

The study enrolled 120 children with Dravet Syndrome. Despite taking an average of three medicines to reduce seizures, the patients were still having a median of 13 seizures per month. The study added Epidiolex or placebo on top of the patients' other anti-seizure medicines.

The most common side effects reported in the study were drowsiness, diarrhea and decreased appetite. Ten Epidiolex patients reported serious adverse events compared with three placebo patients. 

"It would seem like the black cloud that has been raining over the biotech sector as of late is starting to clear as GWPH has reported one of the first major successes of 2016," said Piper Jaffray analyst Josh Schimmer, in a research note Monday. Schimmer has been a consistent GW Pharma bull predicting epidiolex's success. 

GW Pharma bears found reasons to criticize Monday morning's epidiolex data announcement. They raised questions about the sparse details disclosed by the company in the press release, citing the need for more data on the epidiolex's safety profile, how patients who dropped out were counted in the analysis and the drug's interactions with other medicines the patients might be taking. 

GW Pharma is conducting three additional phase III studies of epidiolex, one additional study in Dravet patients and two studies in Lennox-Gastaut Syndrome, another rare form of severe epilepsy. Data read-outs from these studies are expected this year. 

Epidiolex is a liquid formulation of cannabidiol (CBD) derived from marijuana plants which is believed to have anti-epileptic and anti-convulsive activity. 

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