by Scholten A


Seasonal affective disorder (SAD) is a type of depression . It is linked with seasonal changes in light. For most, SAD occurs in late fall and lasts into spring. For others, it starts in the summer and ends in the fall. SAD can cause problems with normal daily functions.

Brain—Psychological Organ
Brain face skull
SAD may be caused by fluctuations in hormones and brain chemicals.
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The exact causes of SAD are not clear. It may be due to:

  • Changes in sunlight—which affects hormones and brain chemicals
  • Changes in melatonin levels—a hormone that plays a role in sleep and mood
  • Changes in serotonin levels—a hormone that controls mood

Risk Factors

SAD is more common in women and young adults. People who live in northern latitudes also have a higher risk of SAD.

Those with depression or bipolar disorder may have a seasonal worsening of depression.


Symptoms of SAD usually appear during winter months. Symptoms tend to disappear in spring and summer. SAD may cause:

  • Low, sad, or irritable feelings
  • Tiredness
  • Sleeping too much or insomnia
  • Social withdrawal
  • Problems focusing
  • Reduced sexual desire
  • Overeating and craving sweet or starchy foods
  • Weight gain


The doctor will ask about your symptoms and health history. A physical and mental health exam will be done.

A diagnosis of SAD is based on symptoms and:

  • If they have occurred for at least 2 years
  • Other major depression has not occurred during the same time
  • Symptoms are gone during summer


The goal of treatment is to ease symptoms. Options are:

  • Light therapy—sitting near an ultra-bright light for a certain time each day
  • Antidepressants—to improve mood
  • Spending time outdoors—to get more sunlight
  • Counseling, such as cognitive-to behavior therapy —to help with coping

Sometimes supplements are used to improve mood. They may include vitamin D and tryptophan. Melatonin may be taken for sleep problems.


If SAD happens each year, the doctor may prescribe bupropion or light therapy to prevent it.


Depression and Bipolar Support Alliance 

Mental Health America 


Canadian Mental Health Association 

Canadian Psychiatric Association 


Galima SV, Vogel SR, et al. Seasonal affective disorder: common questions and answers. Am Fam Physician. 2020;102(11):668-672.

Seasonal affective disorder. EBSCO DynaMed website. Available at: Accessed March 10, 2021.

Seasonal affective disorder. Family Doctor—American Academy of Family Physicians website. Available at: Accessed March 10, 2021.

7/20/06 DynaMed Systematic Literature Surveillance.  : Lam RW, Levitt AJ, et al. The Can-SAD study: a randomized controlled trial of the effectiveness of light therapy and fluoxetine in patients with winter seasonal affective disorder. Am J Psychiatry. 2006;163(5):805-812.

2/16/2016 DynaMed Systematic Literature Surveillance.  : Rohan KJ, Mahon JN, et al. Randomized trial of cognitive-behavioral therapy versus light therapy for seasonal affective disorder: acute outcomes. Am J Psychiatry. 2015 Sep 1;172(9):862-869.

Revision Information

  • Reviewer: EBSCO Medical Review Board Adrian Preda, MD
  • Review Date: 01/2021
  • Update Date: 00/31/2021