What Is Seasonal Affective Disorder (SAD)?

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Seasonal affective disorder (SAD) is a type of depression that is recurrent and seasonally dependent. It is also referred to as major depressive disorder with seasonal pattern in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5).

What Is Seasonal Affective Disorder?

When someone has seasonal affective disorder, they experience depressive symptoms that typically worsen in the fall and winter months, as the days get shorter and darker. In some rarer cases, SAD symptoms can occur in the spring or summer.

Seasonal affective disorder is cyclical. As the seasons change, symptoms go away or change, only to return at the same time each year.

It’s normal to have some fluctuations in mood with the weather, like feeling down on a dreary winter day. As winter approaches, you’re likely to get less sunlight exposure. You may even feel increased stress with the winter holidays, or end-of-year at work.

All of these things can impact your mood, but it’s important to remember that seasonal affective disorder is more than the winter blues. SAD is a recurring form of depression that can feel overwhelming and impact daily functioning—but the good news is it is also common and easily treatable.

Causes of Seasonal Affective Disorder (SAD)

Laura Porter / Verywell


As a subtype of major depressive disorder, seasonal affective disorder has the same symptom profile as depression. The main difference is that these symptoms occur in a seasonal pattern. Symptoms can include:

  • Loss of interest in previous activities or hobbies
  • Social withdrawal
  • Irritability
  • Sadness
  • Anxiety
  • Lack of concentration
  • Fatigue
  • Thoughts of death or suicide

If you are having suicidal thoughts, contact the National Suicide Prevention Lifeline at 988 for support and assistance from a trained counselor. If you or a loved one are in immediate danger, call 911.

For more mental health resources, see our National Helpline Database.

Fall and Winter Symptoms

It is notable that SAD symptoms can differ, depending on the season. Seasonal affective disorder is much more common in winter. Symptoms typical of fall and winter SAD may include:

  • Low energy
  • Overeating
  • Weight gain
  • Craving carbohydrates
  • Increased sleep

Spring and summer seasonal affective disorder is less common, but still occurs. The symptom profile is different, and may include agitation and loss of appetite.


If you think you might have seasonal affective disorder, it’s important to consult with your healthcare provider. They can help you first rule out other conditions that might be causing your symptoms.

To diagnose seasonal affective disorder, your healthcare provider will typically give you a screening questionnaire, such as the Seasonal Pattern Assessment Questionnaire (SPAQ), and a more rigorous interview if indicated.

In order to be diagnosed with seasonal affective disorder, a person must first meet the criteria for major depressive disorder, according to the DSM-5. This means experiencing a minimum of five of the symptoms below, including at least one of the first two symptoms in the list.

These symptoms must be experienced for the majority of the day for at least two continuous weeks:

  • Depressed mood
  • Loss of interest or pleasure in most activities
  • Significant weight and/or appetite changes
  • Sleep disturbances
  • Psychomotor changes
  • Fatigue or low energy
  • Sense of worthlessness
  • Impaired concentration
  • Recurrent thoughts of death or suicidal ideation

Seasonal affective disorder has the same criteria as a major depressive episode, but the symptoms must occur in a seasonal pattern for diagnosis.

Then, to meet the diagnosis for major depressive disorder with seasonal pattern, there are a few more criteria.

First, there must be a full remission of the depressive symptoms at the end of the season. For most people, this would mean starting to feel better in the spring as the sun comes out and weather gets warmer.

Second, there needs to be at least a continuous two-year seasonal pattern to symptoms. During this time, no depressive episode can occur outside of the seasonal period.

And third, there needs to be a lifetime pattern of significantly more seasonal episodes of depression than nonseasonal.


Many people who think they might have seasonal affective disorder actually have subsyndromal seasonal affective disorder (S-SAD). This is a milder form of SAD that is commonly referred to as the “winter blues.”

If you have S-SAD, you might experience some of the symptoms above, but not fit all of the diagnosis criteria for SAD. Even a mild form of seasonal affective disorder can impact your life, though, and you certainly deserve help if this is the case. Many of the treatments for SAD might also help someone with S-SAD.

Subsyndromal seasonal affective disorder (S-SAD) is a milder form of seasonal affective disorder, often called the "winter blues."


In the winter, you might get up before the sun rises, and leave work once the sun has set. Or maybe it’s just too cold to go outside and get some rays. This lack of sunlight can lead to what we experience as seasonal affective disorder.

Like many mental health conditions, the causes of seasonal affective disorder are complex and overlapping. The main theories of causation include serotonin regulation issues, melatonin changes, vitamin D deficiency, and circadian rhythm changes, all stemming from a lack of sunlight:

  • Serotonin regulation: Reduced sunlight leads to a drop in serotoninactivity, which creates depressive symptoms. A 2016 study found that participants with seasonal affective disorder had a failure to down regulate serotonin in the winter, compared to healthy individuals.
  • Melatonin changes: Seasonal changes and lack of sunlight can lead to the overproduction of melatonin, which impacts mood and energy.
  • Circadian rhythm: Less sunlight in the winter can alter the body’s sleep-wake cycle and lead to depressive symptoms.
  • Vitamin D deficiency: Lack of sunshine can lead to low levels of vitamin D, which has been shown to contribute to depression.

Phase Shift Hypothesis (PSH)

The phase shift hypothesis is a theory on the cause of seasonal affective disorder. It posits that lack of sunlight in the winter months leads to a change in the circadian rhythm where people are either “phase advanced” or “phase delayed.”

The majority of people with seasonal affective disorder are phase delayed, which you might recognize as night owl tendencies. These circadian rhythm changes could explain feelings of lethargy, fatigue, and other depressive symptoms experienced during the day.

Risk Factors

You might be more at risk of developing seasonal affective disorder if you have one of these risk factors:

  • Female
  • Live on at a far north or far south latitude
  • Previous major depression or bipolar diagnosis
  • Family history


Seasonal affective disorder is highly treatable. There are a variety of treatment methods for SAD, including light therapy, psychotherapy, and medication.

Light Therapy

Light therapy, also called phototherapy, has long been a central treatment for SAD. It involves using a lightbox, usually in the mornings, for exposure to bright, artificial light. This light mimics the sun and is believed to regulate neurotransmitters and circadian rhythms, thereby reducing feelings of depression.

 A 1984 preliminary study found that phototherapy had an antidepressant effect for people with SAD. This finding was supported by further research over the years, although a later meta-analysis found that much of this research is of low quality, and more rigorous research is needed.

The time of day, strength, and quality of light are all important for effective light therapy. There is no universally acknowledged guideline for light therapy, but research supports:

  • Using light boxes with at least 10,000 lux for 30 minutes
  • Early morning treatment, ideally before 8 a.m. each day
  • Sitting close to the lightbox unit, ideally 16 inches (41 centimeters)
  • Receiving light indirectly through the eyes, usually by placing the lightbox at an angle
  • Starting treatment when symptoms begin in the fall or winter, and stop treatment in the spring and summer

Taking this into account, you could set your lightbox up while doing your morning makeup, or maybe while eating breakfast or drinking your morning coffee. You could also set it behind your computer as you check your morning emails, to ensure the light enters your eyes.

Make sure you set your lightbox unit to 10,000 lux, as well. It’s also wise to start with just a few minutes per day and see how you feel, as light therapy can trigger mania or agitation in some people.

Correct timing, strength, and placement of light therapy are essential to achieving the best results. Current research supports 10,000 lux light therapy for 30 minutes each morning, generally starting in early fall.


Psychotherapy, and specifically cognitive behavioral therapy (CBT), can be an effective treatment for seasonal affective disorder. CBT-SAD is a type of CBT that has been adapted for people with seasonal affective disorder.

In CBT, you’re taught to become aware of your own thoughts, and to replace negative thoughts with more positive thoughts. Through behavioral activation, you’re also taught to identify and engage in behaviors that might help you cope, like an exercise schedule or walking outside each morning.

A 2015 randomized controlled trial compared CBT-SAD to light therapy among people with SAD. The study found that six weeks of CBT-SAD with two 90 minute sessions per week improved depression scores a comparable amount as daily 30 minute 10,000 lux light therapy sessions.

Interestingly, in another study, these same researchers found that two years later, the CBT-SAD group had significantly less recurrence of symptoms than the light therapy group. These findings imply that CBT might be a longer-lasting treatment than light therapy.

The benefits of cognitive behavioral therapy for seasonal affective disorder may be longer lasting than the benefits of light therapy.


Medication is another option for seasonal affective disorder treatment. Selective serotonin reuptake inhibitors (SSRIs) are commonly prescribed.

The Food and Drug Administration (FDA) has also approved Wellbutrin XL (bupropion), which is a norepinephrine-dopamine reuptake inhibitor (NDRI), as a treatment for seasonal affective disorder.

A 2005 randomized prevention trial found that bupropion, compared to a placebo group, could prevent onset of depressive symptoms if administered early in the season before participants became symptomatic.


In addition to the above treatments for seasonal affective disorder, you can also make some lifestyle changes to promote mental wellness in the darker months. These include:

  • Developing a sleep schedule
  • Getting outside each day
  • Exercising regularly
  • Eating a healthy, well-balanced diet

Certain over-the-counter supplements can also help you manage seasonal affective disorder, although you should consult with your healthcare provider on dosages and use.

Vitamin D Supplementation

Vitamin D deficiency has been associated with depression, and supplementing could help improve symptoms. Our main source of vitamin D is from the sun, and sun exposure is at its lowest in the winter months, when seasonal affective disorder is most common.

A 1998 seminal study found that 100,000 I.U. of vitamin D, compared to daily phototherapy, significantly improved depression scores in SAD. However, a later 2006 study on 2,117 older female participants found that daily 800 I.U. of vitamin D supplementation did not improve depression scores.

Although there are mixed results, healthcare providers still often recommend increasing your vitamin D through supplements, sunlight exposure, and incorporating vitamin D rich foods like fish and milk into your diet.

Melatonin Supplementation

Melatonin supplementation could also help improve SAD symptoms, based on the phase shift hypothesis that SAD is related to circadian rhythm changes.

Supplementation with melatonin, similarly to light therapy, can help regulate the circadian rhythm. It’s notable that melatonin can be used for people who are fully blind, who cannot benefit from light therapy.

Dosage amount and time of dosage impact the effectiveness of melatonin, and could lead to adverse effects if taken at the wrong time of day. A 2006 study recommended that an appropriate low dose of melatonin, taken in the afternoon, could improve symptoms, although more research is needed to support those claims.

A Word From Verywell

You're not alone if you feel your mood change with the seasons. However, if you feel symptoms impacting your daily life and functioning, it's worth speaking to your healthcare provider about seasonal affective disorder (SAD) or subsyndromal seasonal affective disorder (S-SAD). There is help available through a variety of evidence-based treatments and seasonal lifestyle changes.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Sarah Bence
Sarah Bence, OTR/L, is an occupational therapist and freelance writer. She specializes in a variety of health topics including mental health, dementia, celiac disease, and endometriosis.