WASHINGTON — A Food and Drug Administration advisory panel on Thursday unanimously recommended approval of an epilepsy medication made with an ingredient found in marijuana. If the agency follows the recommendation, as is expected, the drug would be the first cannabis-derived prescription medicine available in the United States.

The drug, called Epidiolex, is made by GW Pharmaceuticals, a British company. Its active ingredient, cannabidiol, also called CBD, is one of the chemical compounds found in the cannabis plant, but it does not contain the properties that make people high.

That makes it different from the “medical marijuana” allowed by a growing number of states. In those cases, certain patients are legally authorized to smoke or ingest marijuana to treat severe pain, nausea and other ailments.

There are already several drugs on the market that are derived from synthetic versions of THC and other chemicals of the cannabis plant, generally used to ease nausea in cancer patients, and to help AIDS patients avoid weight loss.