An advisory panel to the Food and Drug Administration recommended the agency approve what could become the first prescription drug in the U.S. derived from the marijuana plant, as a treatment for people with rare forms of epilepsy.

A committee on Thursday voted 13-0 that the risk-benefit profile was favorable for GW Pharmaceuticals PLC’s drug, cannabidiol, to treat seizures associated with Lennox-Gastaut syndrome or Dravet syndrome in patients 2 years of age and older. The rare disorders involve frequent or difficult-to-treat...