(Reuters) - The U.S. health regulator approved GW Pharmaceuticals Plc’s epilepsy treatment on Monday, making it the first cannabis-based drug to win approval in the country and opening floodgates for more research into the medicinal properties of cannabis.

FILE PHOTO: A flowering marijuana plant. REUTERS/Chris Wattie

The drug’s approval permits its use in patients aged two 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.

“This approval serves as a reminder that advancing sound development programs that properly evaluate active ingredients contained in marijuana can lead to important medical therapies,” said Food and Drug Administration Commissioner Scott Gottlieb.

The drug, Epidiolex, is made up of cannabidiol (CBD), one of the hundreds of molecules found in the marijuana plant, and contains less than 0.1 percent of tetrahydrocannabinol (THC), the psychoactive component that makes people high.

GW Pharma grows its own supply of cannabis in specialized glass houses in the United Kingdom to ensure uniformity in the genetic composition of the plants, which are then processed into a liquid solution of CBD.

Although THC can induce paranoia, anxiety and hallucinations, CBD has the opposite effect and has been cited by scientists as a potential treatment for mental health issues.

While supporters of legalizing marijuana say the decision is a step in the right direction, businesses reliant on the plant must contend with the federal government’s ban on its use.

Based on the potential for abuse, the Drug Enforcement Administration (DEA) categorizes chemicals into five schedules, with Schedule 1 substances - like marijuana and heroin - considered the most deadly and deemed to have no medical benefits.

As a result, Epidiolex’s launch remains at the discretion of the DEA, which must now evaluate the drug and consider reclassifying it as a substance that has medical properties, so as to allow GW to begin selling it.

GW said it expects the reclassification to occur within 90 days. The company has not yet set a price for the drug and said it would work with insurance providers to ensure the medicine would be covered under health plans.

GW’s Nasdaq-listed shares marginally fell in afternoon trading. The stock has run up nearly 50 percent in the past 12 months.

Most patients with LGS and DS require multiple seizure medications and the majority are resistant to currently approved anti-epileptic drugs.

The two epilepsy forms are severe and associated with high rates of mortality. Some LGS patients have to wear helmets to avoid brain injuries from “drop seizures”, where muscles suddenly become limp and cause standing patients to collapse.

Epidiolex would also be the first approved therapy for DS, treatments for which are currently limited to a combination of seizure medication and drugs to prevent emergencies.

Treatments available for both disorders are far from perfect and some patients resort to buying “self-prescribed” CBD online or from unregulated vendor sites, Dr. Pavel Klein, founder of the Mid-Atlantic Epilepsy and Sleep Center, said.

“I hope patients have conversations with their physicians about whether this product (Epidiolex) provides them with treatment they have been looking for with other unapproved products,” said Douglas Throckmorton, deputy director of regulatory programs at the FDA’s Center for Drug Evaluation and Research.

(This version of the story has been refiled to correct paragraph 12 to show DEA must make a decision within 90 days of FDA approving a medicine, instead of there is no time limit.)