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What: While the broader markets are heading south today on the Brexit vote, shares of GW Pharmaceuticals (NASDAQ:GWPH) gained as much as 12.4% on a positive clinical update for its marijuana-derived epilepsy medicine Epidiolex. Specifically, the company reported that Epidiolex-treated patients suffering from a rare form of childhood epilepsy known as Lennox-Gastaut syndrome (LGS) experienced a significant reduction in drop seizure rate compared to those receiving a placebo. 

So what: Epidiolex has now hit the mark in two late-stage studies, with the drug meeting its primary endpoint in another pivotal trial last March for Dravet syndrome, a severe form of epilepsy that presents in early childhood. The broader issue at play is that clinical evidence actually supporting the use of marijuana-based medicines has been sparse so far due to the drug's Schedule I status. So, GW's late-stage successes for Epidiolex are in many ways breaking new ground. 

Now what: GW is presently conducting a second late-stage study for Epidiolex in LGS that's expected to produce top-line results by the third quarter of 2016. As such, the company could file for the drug's regulatory approval for hard-to-treat childhood epilepsies perhaps as early as the first quarter of 2017.

While that's all well and good, it's next to impossible to predict how the FDA is going to handle a regulating filing for a marijuana-derived medicine. After all, the agency has little real-life experience with these types of pharma products, and the debate over the medical benefits of marijuana -- or its derivatives -- is far from resolved. I think GW's stock is still trading almost purely on speculation, meaning that investors may want to stick to the sidelines with this high-flying marijuana stock for the moment.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.