NORTHAMPTON, Mass. — LAST week, Sprout Pharmaceuticals resubmitted its drug flibanserin to the Food and Drug Administration for approval. Flibanserin, in case you haven’t heard, is a drug intended to treat low sexual desire in women. The F.D.A. has rejected it twice already, and will most likely reject it a third time because (if you’re Sprout) the F.D.A. is sexist or (if you’re the F.D.A.) the drug doesn’t work and isn’t safe.

But the biggest problem with the drug — and with the F.D.A.’s consideration of it — is that its backers are attempting to treat something that isn’t a disease.

Flibanserin purportedly treats a condition called hypoactive sexual desire disorder in women. But H.S.D.D. was removed from the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders in 2013, and replaced with a new diagnosis called female sexual interest/arousal disorder, or F.S.I.A.D.

Why the change? Researchers have begun to understand that sexual response is not the linear mechanism they once thought it was. The previous model, originating in the late ’70s, described a lack of “sexual fantasies and desire for sexual activity.” It placed sexual desire first, as if it were a hunger, motivating an individual to pursue satisfaction. Desire was conceptualized as emerging more or less “spontaneously.” And some people do feel they experience desire that way. Desire first, then arousal.