Made by the British biopharma company GW Pharmaceuticals, Epidiolex uses purified cannabidiol, or CBD, which is one of more than 80 active compounds in the cannabis sativa plant, often known simply as marijuana.
The move marks several firsts.
Parents already use CBD oil to treat their children with epilepsy, so Epidiolex is a pharmaceutical-grade type of CBD oil.
The drug is derived from the cannabidiol of cannabis, and, as the plant is yet to be decriminalized by federal regulators, its approval gives GW Pharma a lead among cannabis-exposed companies in the USA financial markets.
US Food and Drug Administration Commissioner Dr Scott Gottlieb said: "This is an important medical advance. Because of the adequate and well-controlled clinical studies that supported this approval, prescribers can have confidence in the drug's uniform strength and consistent delivery".
The two forms of epilepsy that are covered by the approval are Lennox-Gastaut syndrome and Dravet syndrome in patients, aged two years or more.
Patients who received CBD in three randomized, double-blind clinical trials saw much bigger improvements than patients who received placebos. However, Epidiolex does not contain THC, the component of marijuana that gets people high, Jamie Alan, an assistant professor of pharmacology and toxicology at Michigan State University, tells Yahoo Lifestyle. Outside the USA, this medicine is now under review by the European Medicines Agency (EMA) for the treatment of seizures associated with Dravet Syndrome and LGS.
Even though there are numerous approved epilepsy drugs, Dr. Devinsky says there's a pressing need for something like Epidiolex because it has a completely different, and better tolerated, formula for patients.
Epidiolex is approved to treat Lennox-Gastaut syndrome and Dravet syndrome in patients two years and older, the FDA said. These side effects are "sleepiness, sedation and lethargy; elevated liver enzymes; decreased appetite; diarrhea; rash; fatigue, malaise and weakness; insomnia, sleep disorder and poor quality sleep; and infections".
"Today's approval demonstrates our commitment to the scientific process and working with product developers to bring marijuana-based products to market", he said.
This one landmark approval could have another one following it soon: the reclassification of CBD by the United States Drug Enforcement Administration. 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.