Health Condition

Seasonal Affective Disorder

About This Condition

Seasonal affective disorder (SAD) is an extreme form of common seasonal mood cycles, in which depression develops during the winter months.

How seasonal changes cause depression is unknown, but most of the research into mechanisms and treatment has focused on changes in levels of the brain chemicals melatonin and serotonin in response to changing exposure to light and darkness.


SAD is characterized by typical symptoms of depression, such as sadness, hopelessness, and thoughts of suicide (in some cases), and “atypical” depressive symptoms such as excessive sleep, lethargy, carbohydrate cravings, overeating, and weight gain. The symptoms usually occur the same time of year, typically fall and winter, and disappear with the onset of spring and summer.

Light exposure research and treatment measures in “lux” units. For example, the intensity of light on a high mountain at the equator at midday is greater than 100,000 lux, compared with less than 11 lux generated by a moonlit night. A well-lit kitchen or office may be around 500 lux.

Other Therapies

Treatment includes daily exposure to bright light, often 2,500 lux administered in two-hour increments. Individuals with SAD should spend as much time as possible outside during the day. Use of a “dawn simulator,” a light programmed to slowly increase in intensity in the morning, is also recommended. Some healthcare providers might also recommend aerobic exercise under bright lights.


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The information presented by Healthnotes is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. Self-treatment is not recommended for life-threatening conditions that require medical treatment under a doctor's care. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires December 2018.

Drugs used to treat SEASONAL AFFECTIVE DISORDER. Select drug name to view medication information and pricing