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Seasonal affective disorder: Epidemiology, clinical features, assessment, and diagnosis

David Avery, MD
Section Editor
Peter P Roy-Byrne, MD
Deputy Editor
David Solomon, MD


The term seasonal affective disorder (SAD) describes episodes of major depression, mania, or hypomania that regularly occur during particular seasons. The most prevalent form of SAD is winter depression, marked by recurrent episodes of unipolar depression that begin in the fall or winter and, if left untreated, generally remit in the following spring or summer. Recognizing the disorder is important because SAD is common and associated with psychosocial impairment [1,2]. In addition, acute treatment is often effective and maintenance treatment can prevent future episodes [3]. Among patients who were recruited for randomized trials studying treatment of winter depression, nearly 60 percent had never been treated for depression [4].

This topic discusses the epidemiology, pathogenesis, clinical features, assessment, diagnosis, and validity of SAD; most of the topic is devoted to recurrent unipolar major depression with winter seasonal pattern (winter depression). Choosing treatment is reviewed separately. (See "Seasonal affective disorder: Treatment".)


Seasonal affective disorder — Seasonal affective disorder (SAD) is defined as recurrent episodes of major depression, mania, or hypomania with seasonal onset and remission [5]. It is not considered a separate mood disorder; rather, SAD is a subtype of the following mood disorders:

Unipolar major depression (major depressive disorder)

Bipolar I disorder


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