RESEARCH TRIANGLE PARK, N.C. — The Food and Drug Administration approved on Monday a GlaxoSmithKline drug for the treatment of seasonal affective disorder, or SAD, that affects some 13 million adults.

The disorder is often called “winter blues”

The drug is called Wellbutrin. It is the first drug approved to prevent seasonal major depressive episodes that strike primarily during the winter. Three clinical trials demonstrated that Wellbutrin reduces the chance of developing a depressive episode by 44 percent.