GW Pharma says cannabis-based epilepsy drug meets main goal

British drug developer GW Pharmaceuticals Plc said its experimental cannabis-derived epilepsy drug met the main goal to reduce frequency of seizures in a late-stage study.

Shares of the company were up about 21 percent at 611 pence at 11.33 GMT (7.33 a.m. ET) on the London Stock Exchange. GW Pharma's U.S.-listed shares were up nearly 17 percent at $96.52 on the Nasdaq in premarket trading on Monday.

The company said the drug, Epidiolex, significantly reduced the monthly frequency of short-term seizures in people suffering from a rare form of epilepsy called Lennox-Gastaut syndrome (LGS).

Lennox-Gastaut syndrome is a rare kind of epilepsy that shows onset between 3-5 years of age. GW Pharma estimates there are about 14,000-18,500 patients with LGS in the United States, and 23,000-31,000 in Europe.

GW Pharma is testing Epidiolex in four different indications, three of which are forms of epilepsy and all three have been granted orphan drug designation from the U.S. Food and Drug Administration.

Orphan status is granted to drugs aimed at treating rare diseases, giving the developer incentives such as a seven-year marketing exclusivity in the United States.

(Reporting by Vidya L Nathan in Bengaluru; Editing by Shounak Dasgupta)