Of the 16 million American adults who live with depression, as many as one-quarter gain little or no benefit from available treatments, whether drugs or talk therapy. They represent perhaps the greatest unmet need in psychiatry. On Tuesday, the Food and Drug Administration approved a prescription treatment intended to help them, a fast-acting drug derived from an old and widely used anesthetic, ketamine.

The move heralds a shift from the Prozac era of antidepressant drugs. The newly approved treatment, called esketamine, is a nasal spray developed by Janssen Pharmaceuticals Inc., a branch of Johnson & Johnson, that will be marketed under the name Spravato. It contains an active portion of the ketamine molecule, whose antidepressant properties are not well understood yet. "Thank goodness we now have something with a different mechanism of action than previous antidepressants," said Dr. Erick Turner, a former F.D.A. reviewer and an associate professor of psychiatry at Oregon Health & Science University. "But I'm skeptical of the hype, because in this world it's like Lucy holding the football for Charlie Brown: Each time we get our hopes up, the football gets pulled away."

[...] Esketamine, like ketamine, has the potential for abuse, and both drugs can induce psychotic episodes in people who are at high risk for them. The safety monitoring will require doctors to find space for treated patients, which could present a logistical challenge, some psychiatrists said.

The wholesale cost for a course of treatment will be between $2,360 and $3,540, said Janssen, and experts said it will give the company a foothold in the $12 billion global antidepressant market, where most drugs now are generic.

[...] One question that will need to be answered is how well esketamine performs in comparison to intravenous ketamine.