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Seasonal affective disorder (SAD) cannot be cured, but its symptoms can be treated effectively. Light therapy provided by bright, white, fluorescent bulbs is the primary treatment for SAD. These lights have color temperatures between 3,000 and 6,500 degrees Kelvin and are used in lamps surrounded by a box with a diffusing lens. This helps to filter out potentially harmful ultraviolet radiation. The lower color temperatures used in light therapy produce a soft, white light and the high color temperatures produce a colder light similar to the light in the sky.

Patients place the box on a tabletop with a stand that raises the light to eye level or above. This helps to both reduce glare and concentrate the light on the lower half of the retina, an area of the eye that has photoreceptors that appear to be involved in the antidepressant response. Patients should not stare directly into the light. In some cases, the light may be delivered through a visor device.

Sessions often are conducted in the morning and typically last for 30 minutes or more. Light therapy dosages are individualized for the patient, according to the intensity of light, the duration and the time of day of light exposure. Lights used in tanning beds are not effective for light therapy, as they fail to filter out ultraviolet rays.

Light therapy is often extremely effective. The lights used are 10 to 20 times brighter than typical indoor lights. Studies have shown that it helps reduce the production of the hormone melatonin, which has been linked to higher rates of depression. Between 50 and 80 percent of patients who undergo light therapy see their symptoms disappear completely, according to the National Alliance on Mental Illness (NAMI). In many cases, patients will begin to feel better after just a few days of light therapy, although it may take as long as a month in some cases. Treatments must be continued throughout the season that causes the symptoms.

Side effects associated with light therapy are uncommon and relatively minor. They may include irritability, eyestrain, headaches and nausea. However, patients with a history of bipolar disorder should approach light therapy with caution, as they may be at increased risk of experiencing altered mood states. Patients who take medications that make them sensitive to light also may not be good candidates for light therapy.

Antidepressants are also sometimes prescribed for patients with SAD and appear to be as effective as light therapy. In June 2006, the U.S. Food and Drug Administration (FDA) approved the use of bupropion HCL for the treatment of SAD. Another antidepressant that has shown to be effective in the treatment of the depressive disorder in clinical trials is fluoxetine. Patients who have a history of SAD may be put on antidepressant therapy shortly before the season that typically triggers symptoms, and discontinue the medication shortly after the season ends. Patients may not feel the benefits of antidepressants until between two to four weeks after they begin taking them.

The FDA has advised that antidepressants may increase the risk of suicidal thinking in some patients, particularly children and adolescents, and all people being treated with them should be monitored closely for unusual changes in behavior.