* FDA panel votes 13-0 in favor of GW's drug
* Cowen analysts expect $1.3 bln in sales by 2022 (Adds details, analyst comment, estimates, background)
By Manas Mishra
April 19 (Reuters) - An advisory panel to the U.S. Food and Drug Administration on Thursday unanimously voted in favor of approving the first cannabis-derived medicine in the country, a childhood epilepsy treatment developed by GW Pharma.
The drug, Epidiolex, is derived from cannabidiol (CBD), one of the hundreds of molecules found in the marijuana plant, and an FDA decision is expected by June 27.
The syrup contains less than 0.1 percent of tetrahydrocannabinol (THC), the substance that makes people high.
The FDA panel found that the drug's benefits outweighed the risks to treat patients aged 2 years and older with Dravet Syndrome (DS) and Lennox-Gastaut Syndrome (LGS), rare childhood-onset forms of epilepsy that are among the most resistant to treatment.
The agency does not have to act on the recommendations of its experts, but usually does.
"The overall tone of the meeting was positive, with the FDA having identified no obstacles to approval," Cantor Fitzgerald analyst Elemer Piros said, adding that he expects the drug will be approved much before June 27.
Cowen analysts forecast sales of $1.3 billion for the drug by 2022.
The panel's backing comes after the FDA staff on Tuesday gave a favorable review, citing three clinical studies that showed the drug reduced frequency of seizures in patients with the disease when added to a current therapy.
Analysts said an approval will also confirm the therapeutic benefits of CBD. "This should aid CBD in being efficiently rescheduled by the Drug Enforcement Administration," said Cowen & Co analyst Phil Nadeau on Tuesday.
Under the U.S. federal law, marijuana is considered to have no medicinal value.
However, the FDA panel highlighted the limited association between the use of CBD and elevated liver enzymes, which Cantor Fitzgerald's Piros believe could lead to a boxed warning label, the severest form of FDA warning.
It is estimated there are about 14,000-18,500 patients with LGS, and 1 in 40,000 sufferers of Dravet Syndrome in the United states, for which there is no approved treatment.
Some LGS patients have to wear helmets to avoid brain injuries from "drop seizures" that cause loss of muscle strength.
U.S. shares of the U.K.-based company was trading flat at $132.23 by afternoon. (Reporting by Manas Mishra in Bengaluru; Editing by Sriraj Kalluvila)