A summary of information on seasonal affective disorder for patients from the US Dept. of Mental Health and Substance Abuse Disorders. James W. Mold, MD, MPH

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What is seasonal affective disorder?

Many people go through short periods when they feel sad or unlike their usual selves. Sometimes, these mood changes begin and end when the seasons change. Many people feel "down" or have the "winter blues" when the days get shorter in the fall and winter and feel better in the spring when longer daylight hours return.

Sometimes, these mood changes are more serious and can affect how a person feels, thinks, and behaves. If you have noticed significant changes in your mood and behavior when the seasons change, you may be experiencing seasonal affective disorder (SAD).

In most cases, SAD symptoms start in the late fall or early winter and go away during the spring and summer, known as winter-pattern SAD or winter depression. Other people experience depressive symptoms during the spring and summer months, known as summer-pattern SAD or summer depression. Summer-pattern SAD is less common.