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Seasonal affective disorder (SAD)

Reviewed by Robert Bogenberger, PhD

A woman looking out a window during winter.

What Is Seasonal Affective Disorder?

Do the winter months give you the blues? If so, you might have seasonal affective disorder (SAD), which is now called major depressive disorder with a seasonal pattern. Seasonal affective disorder is also sometimes called seasonal depression.

Seasonal affective disorder typically occurs during the winter months. SAD most often affects those who live farther from the equator and experience darker winter months with less sunshine and light.

About 3% to 5% of the population experiences seasonal affective disorder.1 Another 10% to 15% of people may experience a milder form of seasonal mood changes.

Seasonal Affective Disorder Causes

Therapists, physicians, and scientists don’t fully understand the root causes of SAD. One theory is that the reduced level of sunlight during the winter months triggers a chemical change in the brain. Lower levels of vitamin D in particular can cause the brain to make less serotonin during the winter months, leading to depression.

Another theory is that the body’s circadian rhythm changes in response to the reduced sunlight, contributing to changes in mood. Some experts also suggest that those who experience SAD may produce too much melatonin, a hormone that helps regulate the wake-sleep cycle. Delayed sleep timing, which occurs when sleep is delayed two or more hours from a conventional sleep pattern, has been shown to be a characteristic of SAD.2 

While the exact causes of seasonal affective disorder are still unknown, it does occur more frequently during the winter (although summer cases can happen), and it tends to occur more frequently for people who live farther from the equator. Other risk factors include:

  • Having major depressive disorder
  • Having bipolar disorder
  • Being female
  • Having a family member with SAD 
  • Having a family history of mental illness

Seasonal Affective Disorder Symptoms

SAD can affect each person differently, but many symptoms are similar to those of depression. Many people who experience SAD have symptoms that happen around the same time each year.

Winter symptoms can include:

Summer symptoms can include:

Diagnosing Seasonal Affective Disorder

Because the symptoms of SAD are similar to other mood disorders, it can take some time to rule out other causes and receive a SAD diagnosis. The criteria for being diagnosed with SAD come from the DSM-5:

  • Having the symptoms of major depression
  • Experiencing depressive episodes that occur during specific seasons for at least two years
  • Having said episodes occur more frequently than other depressive episodes at other times

There is no test that can accurately diagnose SAD. Instead, your therapist will ask questions about your symptoms to determine whether they meet the criteria for seasonal affective disorder. It is important to note that there can be seasonal events that can worsen depression, such as losing one’s job during the winter or children leaving for school. If these are causing the worsened symptoms, this is a different issue than SAD.

Depression vs. Seasonal Affective Disorder

Because seasonal affective disorder is a type of major depressive disorder, the symptoms of depression are similar to those of SAD. The key difference between the two is that people with SAD experience a pattern where their depressive symptoms appear during the winter months. 

People with SAD experience worsening symptoms during the fall and winter, and their symptoms generally improve as spring approaches. People with depression do not experience this same seasonal pattern to their depressive episodes.

Seasonal Affective Disorder Treatment

SAD can be treated in a variety of ways. Some of the more common treatments include light therapy, cognitive behavioral therapy (CBT), and medications. In some cases, a combination of treatments may be used to help reduce symptoms. Your therapist will determine the best course of action for your particular symptoms and experiences with SAD.

Healthy lifestyle changes can also help someone with SAD better manage their symptoms in combination with other therapies. Prioritizing exercise, sleep, and nutrition can all help someone with SAD.

Seasonal Affective Disorder (SAD) Light Therapy

Studies have found that light therapy can be an effective treatment for seasonal affective disorder.3 Seasonal affective disorder light therapy involves the use of a special box that mimics natural light. The individual sits in front of this box for a specified amount of time each day, and the light indirectly shines on the person’s eyes. 

It’s important that light therapy only be used under the direction of a trained professional because using the box improperly can cause eye damage. Generally, ultraviolet lamps or tanning lamps will not have the same effect for clients with SAD as a light therapy box.

Another related therapy that is sometimes used is a dawn simulator. This device is a time-activated light that is used to mimic sunrise. This can help regulate the body’s circadian rhythm. 

Some people find that exposure to natural light is helpful. Planning winter activities outside (when possible), letting more natural light inside by opening curtains, or sitting closer to windows during the daytime can help someone with SAD.


Psychotherapy is another commonly used treatment for SAD. Therapies like CBT can help people recognize and better manage their SAD symptoms. Both individual and group sessions can be helpful for dealing with SAD. Therapy can help people not only modify negative thoughts about the winter months but also adapt new behaviors that are beneficial for those experiencing SAD.

Medication and Supplementation

In some cases, medications may be prescribed to help people with SAD. Antidepressants like Zoloft and Prozac may be used to help reduce symptoms. Bupropion has also been approved by the FDA for use with SAD.

Some people also may benefit from the use of supplements such as vitamin D and melatonin to improve their sleep and circadian rhythms. 

Getting Help for Seasonal Affective Disorder

If you experience symptoms of depression during the fall and winter, you may have SAD. Reach out to a therapist who specializes in SAD to discuss your symptoms and possible treatment options.

About the author

The editorial team at works with the world’s leading clinical experts to bring you accessible, insightful information about mental health topics and trends.

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