(CNN) The US Food and Drug Administration approved a cannabis-based drug for the first time, the agency said Monday.

Epidiolex was recommended for approval by an advisory committee in April, and the agency had until this week to make a decision.

The twice-daily oral solution is approved for use in patients 2 and older to treat two types of epileptic syndromes: Dravet syndrome, a rare genetic dysfunction of the brain that begins in the first year of life, and Lennox-Gastaut syndrome, a form of epilepsy with multiple types of seizures that begin in early childhood, usually between 3 and 5.

"This is an important medical advance," FDA Commissioner Dr. Scott Gottlieb said in a statement Monday. "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 drug is the "first pharmaceutical formulation of highly-purified, plant-based cannabidiol (CBD), a cannabinoid lacking the high associated with marijuana, and the first in a new category of anti-epileptic drugs," according to a statement Monday from GW Pharmaceuticals, the UK-based biopharmaceutical company that makes Epidiolex.

Cannabidiol is one of more than 80 active cannabinoid chemicals, yet unlike tetrahydrocannabinol, or THC, it does not produce a high.

The FDA has approved synthetic versions of some cannabinoid chemicals found in the marijuana plant for other purposes, including cancer pain relief.

Justin Gover, chief executive officer of GW Pharmaceuticals, described the approval in the statement as "a historic milestone." He added that the drug offers families "the first and only FDA-approved cannabidiol medicine to treat two severe, childhood-onset epilepsies."

"These patients deserve and will soon have access to a cannabinoid medicine that has been thoroughly studied in clinical trials, manufactured to assure quality and consistency, and available by prescription under a physician's care," Gover said.

Epidiolex will become available in the fall, Gover told CNN. He would not give any information on cost, saying only that it will be discussed with insurance companies and announced later.

With Epidiolex meeting FDA standards, the drug will "finally be made available to the thousands that may benefit from it," he said.

According to the Epilepsy Foundation, up to It's an option for those patients who have not responded to other treatments to control seizures.According to the Epilepsy Foundation, up to one-third of Americans who have epilepsy have found no therapies that will control their seizures.

Shauna Garris, a pharmacist, pharmacy clinical specialist and adjunct assistant professor at the University of North Carolina's Eshelman School of Pharmacy, said the drug is effective and works somewhere between "fairly" and "very well." She has not used Epidiolex in her own clinical practice and was not involved in the development of the drug but said she's not sure it will live up to "all of the hype" that has surrounded it.

There are side effects, the most common being sleepiness, Gover said. But Garris highlighted that many of the side effects occur when it is taken with other medications, which she said is a concern because most patients are on other medications.

There are likely to be drug interactions, she said, but "that's not uncommon for antiepileptic medications," and she noted that this could affect the effectiveness of the medication.

The European Medical Society is also considering approval of Epidiolex and is expected to announce a decision in the first quarter of next year, according to Gover.

A phase three clinical trial is underway for a third seizure-related condition called tuberous sclerosis complex, which begins in infancy and causes a sudden stiffening of the body, arms and legs, with the head bent forward. Glover said that if the results are positive, his company will apply for supplemental approval for this condition.

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In the meantime, it is possible that once on the market, Epidiolex could be prescribed for conditions other than the ones it's approved for. This is called off-label use and is a common practice with many medications.

As part of the FDA's review of the medication, the potential for abuse was assessed and found to be low to negative, according to Gover.

Still, this approval comes as the White House is said to be reconsidering federal prohibition of marijuana and as more and more states approve it for recreational and medicinal use.

Gover said the approval signals "validation of the science of cannabinoid medication."