(CNN) A US Food and Drug Administration advisory committee on Thursday unanimously recommended approval of an epilepsy drug that would be the first plant-derived cannabidiol medicine for prescription use in the United States.

The FDA will vote in June whether to approve the drug, Epidiolex, an oral solution, for the treatment of severe forms of epilepsy in a small group of patients. The FDA has approved synthetic versions of some cannabinoid chemicals found in the marijuana plant for other purposes, including cancer pain relief.

The committee's recommendation was delivered after reviewing data from the drug's maker, GW Pharmaceuticals PLC, a UK-based biopharmaceutical company.

"We're obviously very pleased by the unanimous recommendation in support of the approval of Epidiolex," GW CEO Justin Gover said. "It's a very important milestone in the approval process."

Epidiolex, GW's lead cannabinoid product candidate, was developed for severe, early-onset epilepsy syndromes , including Dravet syndrome, a rare genetic dysfunction of the brain that begins in the first year of life; Lennox-Gastaut syndrome, a type of epilepsy with multiple types of seizures; and tuberous sclerosis complex and infantile spasms, both of which begin in infancy and cause a sudden stiffening of the body, arms and legs with the head bent forward.

One-third of Americans who have epilepsy have found no therapies that will control their seizures, according to the Epilepsy Foundation . This represents about 1 million families.

Though FDA approval would limit use of the drug to epilepsy patients, doctors would have the option to prescribe it "off-label" for other uses.

Shauna Garris, a pharmacist, pharmacy clinical specialist and adjunct assistant professor at the University of North Carolina's Eshelman School of Pharmacy, said she would be surprised if Epidiolex does not get full approval from the FDA. Garris was not involved in the development of the drug and has not used it in her own clinical practice.

Still, she said, "there's so much publicity and so much hype" surrounding the product, she's not sure it will live up to "all that hype."

Epidiolex is effective, she said, working somewhere between "fairly" and "very well."

"There have been side effects associated with it, and it appears a lot of the side effects were in conjunction with other medications, which is a concern, because most of those patients are on other medications," Garris said. There are likely to be drug interactions, she said, but "that's not uncommon for antiepileptic medications."

"Most of our antiepileptic medications have terrible side effects and interact with each other," she said. Still, this may impact potential efficacy.

In a statement, GW Pharmaceuticals said that two experimental clinical trials, one in Dravet syndrome and one in Lennox-Gastaut syndrome, showed "significantly greater reductions" in certain seizure types for patients taking Epidiolex compared with those taking a placebo.

During the public hearing at Thursday's advisory committee meeting, 16-year-old Sam Vogelstein of Berkeley, California, described himself as "the first person to try Epidiolex for epilepsy." He said he was not paid by the company to speak Thursday.

"I had seizures for 10 years," he said. "My parents tell me there were times I had seizures 100 times a day." He began Epidiolex five years ago. "I've been seizure-free for more than two years now. It changed my life."

Damage to the liver, which metabolizes drugs and detoxifies chemicals, is an important consideration during the recommendation process of any medicine.

Dr. Lara Dimick-Santos, a clinical reviewer in the FDA's Office of Drug Evaluation, reviewed the liver safety report and concluded that there were "no cases of severe liver injury" and "no deaths related with liver injury." She suggested, though, that some patients might experience some form of "unknown of chronic liver injury." Such a "smoldering inflammatory response" could "potentially cause a problem for patients further down the line."

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Katherine Bonson, a member of the FDA's Pharmacologist Controlled Substance Staff, assessed the abuse potential for cannabidiol after looking at both animal and human experimental data. "Overall conclusion, preclinical data do not provide signals that CBD has abuse potential," she said.

Though the FDA stressed that review of Epidiolex will be ongoing, Gover said he feels confident about a positive outcome. "It's a breakthrough in the field of epilepsy," he said. "It's the first cannabis-based pharmaceutical to be approved by the FDA. It's the first in a new class of treatments with a new mechanism of action against epilepsy."