Seasonal Affective Disorder



  • Seasonal affective disorder (SAD) describes mood episodes that occur as a part of major depressive or bipolar disorder in a seasonal pattern. Patients may more commonly experience depressive or less commonly hypomanic to manic episodes.
  • Depressive episodes typically occur during winter months (fall-winter onset), with full remission in the spring and summer. Less commonly, patients may experience a spring-summer onset with remission in the fall-winter months.
  • Ranges from a milder form (winter blues) to a seriously disabling illness



  • Affects up to 500,000 Americans every winter
  • Up to 30% of patients visiting a primary care physician (PCP) during winter may report winter depressive symptoms.
  • Predominant age: occurs at any age; peaks in 20s and 30s
  • Predominant sex: female > male (3:1)

Etiology and Pathophysiology

  • Photoperiod and phase shift hypothesis note that during the winter months, the period of natural daylight is shorter. When there is less sunlight, the pineal gland increases melatonin secretion, which can lead to a phase shift in circadian rhythm. This process has been linked to symptoms of depression. Light therapy in the morning or evening can suppress melatonin secretion to correct the phase shift and improve symptoms of depression. Reduced sunlight may also decrease vitamin D levels, which may contribute to symptoms of depression.
  • Serotonin dysregulation hypothesis is a suspected dysregulation of serotonin, particularly increased clearance from the synaptic cleft and reduced secretion, contributes to SAD pathophysiology. Central acting serotonergic agents such as SSRIs appear to reverse SAD symptoms.


  • Twin studies suggest a genetic component.
  • Studies also indicate an association with melanopsin gene (OPN4) and GPR50 melatonin receptor variants.

Risk Factors

  • Most common during months of January and February
  • Working in a building without windows or other environments without significant sunlight exposure

General Prevention

  • Consider use of light therapy at the start of winter (if prior episodes begin in October), increase time outside during daylight hours, or move to a more southern location.
  • Bupropion (Wellbutrin) is the only FDA-approved antidepressant for the prevention of SAD.
  • Although studies show mixed results, low-dose evening melatonin may help prevent symptoms of depression from occurring.

Commonly Associated Conditions

Comorbid psychiatric disorders such as alcohol use disorder, ADHD, and binge eating

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