The Food and Drug Administration on Monday gave the nod to a drug with the potential to provide the first systemic treatment of alopecia areata, a hair-loss condition. The drug, an oral pill known as baricitinib made by Eli Lilly, was already on the market under the name Olumiant as a treatment for other autoimmune disorders like rheumatoid arthritis, according to the company. In two large phase III trials sponsored by Lilly and published earlier this year, nearly 40 percent of 1,200 patients with severe alopecia areata experienced total or near-total hair regrowth after 36 weeks of taking baricitinib, which blocks the immune system from destroying the body’s hair follicles. After a year in the trials, close to half the patients experienced regrowth. Baricitinib is the first of its class, known as JAK inhibitors, to be approved for the treatment of alopecia, though at least two other drugs are currently being studied in clinical trials. As many as 300,000 people are thought to have severe alopecia areata in the U.S. alone, with hair loss affecting more than 6 million more.