Seasonal affective disorder (SAD) is a sub-disorder under depressive disorders. It is a pattern of major depressive episodes that occurs in line with seasonal changes. Winter-type seasonal pattern is most common, especially in higher latitudes. Summer-type seasonal pattern is less often diagnosed, but also occurs in some people.

The essential feature is the onset and remission of major depressive episodes at characteristic times of the year — often with the change of the seasons (e.g., from fall into winter, or from winter into summer). Formerly known (in the previous diagnostic manual, the DSM-IV) as seasonal affective disorder (SAD), in most cases the episodes begin in fall or winter and remit in spring. Less commonly, there may be recurrent summer depressive episodes.

This pattern of onset and remission of episodes must have occurred during at least a 2-year period, without any nonseasonal episodes occurring during this period. In addition, the seasonal depressive episodes must substantially outnumber any nonseasonal depressive episodes over the individual’s lifetime.

Lots of people feel temporarily blue about the changing of the seasons for a day or two. People who have a passing feeling of sadness, feeling lonely or down generally wouldn’t quality for a diagnosis of seasonal affective disorder (SAD). The depressive episode must last for at least two (2) complete weeks in order to be diagnosed as a major depressive episode, and must occur every day, for most of the day throughout that time.

People who suffer from a depressive disorder with seasonal pattern generally lose interest or pleasure in most daily activities, may have significant weight gain and engage in regular overeating, and trouble falling or staying asleep, but with a constant feeling of energy throughout the day, most days. Feelings of worthlessness and feelings of guilt may be common, as well as an inability to think or concentrate, or finish tasks at work or school. Some people even experience recurrent thoughts of death.

This specifier does not apply to those situations in which the pattern is better explained by seasonally-linked psychosocial stressors (e.g., seasonal unemployment or school schedule).

Major depressive episodes that occur in a seasonal pattern are characterized by:

  • Prominent energy
  • Hypersomnia
  • Overeating
  • Weight gain
  • Craving carbohydrates

It is unclear whether a seasonal pattern is more likely in recurrent major depressive disorder or in bipolar disorders. Age is also a strong predictor of seasonality, with younger persons at higher risk for winter depressive episodes.

Learn more: Seasonal Affective Disorder Treatment

This entry has been adapted for DSM-5.