Seasonal

Affective

Disorder

What is seasonal affective disorder?

Many people go through short periods of time where 

they feel sad or not like their usual selves. Sometimes, 

these mood changes begin and end when the seasons 

change. People may start to feel “down” when the 

days get shorter in the fall and winter (also called 

“winter blues”) and begin to feel better in the spring, 

with longer daylight hours. 

In some cases, these mood changes are more serious 

and can affect how a person feels, thinks, and handles 

daily activities. If you have noticed significant changes 

in your mood and behavior whenever the seasons 

change, you may be suffering from seasonal affective 

disorder (SAD), a type of depression. 

In most cases, SAD symptoms start in the late fall 

or early winter and go away during the spring and 

summer; this is known as winter-pattern SAD or winter 

depression. Some people may experience depressive 

episodes during the spring and summer months; this is 

called summer-pattern SAD or summer depression 

and is less common. 

What are the signs and 

symptoms of SAD?

SAD is not considered a separate disorder but is a type 

of depression characterized by its recurrent seasonal 

pattern, with symptoms lasting about 4 to 5 months 

per year. Therefore, the signs and symptoms of SAD 

include those associated with major depression, and 

some specific symptoms that differ for winter-pattern 

and summer-pattern SAD. Not every person with SAD 

will experience all of the symptoms listed below.

Symptoms of major depression may include: 

● Feeling depressed most of the day, nearly every day

● Losing interest in activities you once enjoyed

● Experiencing changes in appetite or weight

● Having problems with sleep

● Feeling sluggish or agitated

● Having low energy

● Feeling hopeless or worthless

● Having difficulty concentrating

● Having frequent thoughts of death or suicide

For winter-pattern SAD, additional specific symptoms 

may include: 

● Oversleeping (hypersomnia)

● Overeating, particularly with a craving for carbohydrates

● Weight gain

● Social withdrawal (feeling like “hibernating”)

Specific symptoms for summer-pattern SAD 

may include: 

● Trouble sleeping (insomnia)

● Poor appetite, leading to weight loss

● Restlessness and agitation

● Anxiety

● Episodes of violent behavior

If you or someone you know is in immediate distress 

or is thinking about hurting themselves, call the 

National Suicide Prevention Lifeline toll-free at 

1-800-273-TALK (8255) or the toll-free TTY number 

at 1-800-799-4TTY (4889). You also can text the 

Crisis Text Line (HELLO to 741741) or go to the 

National Suicide Prevention Lifeline website at 

https://suicidepreventionlifeline.org.

Get Immediate Help

From the NATIONAL INSTITUTE of MENTAL HEALTH
How is SAD diagnosed? 

If you think you may be suffering from SAD, talk 

to your health care provider or a mental health 

specialist about your concerns. They may have you 

fill out specific questionnaires to determine if your 

symptoms meet the criteria for SAD. 

To be diagnosed with SAD, a person must meet the 

following criteria:

● They must have symptoms of major depression or 

the more specific symptoms listed above. 

● The depressive episodes must occur during 

specific seasons (i.e., only during the winter months 

or the summer months) for at least 2 consecutive 

years. However, not all people with SAD do 

experience symptoms every year.

● The episodes must be much more frequent 

than other depressive episodes that the person 

may have had at other times of the year during 

their lifetime. 

Who develops SAD? 

Millions of American adults may suffer from SAD, 

although many may not know they have the 

condition. SAD occurs much more often in women 

than in men, and it is more common in those living 

farther north, where there are shorter daylight hours 

in the winter. For example, people living in Alaska or 

New England may be more likely to develop SAD 

than people living in Florida. In most cases, SAD 

begins in young adulthood. 

SAD is more common in people with major 

depressive disorder or bipolar disorder, especially 

bipolar II disorder, which is associated with recurrent 

depressive and hypomanic episodes (less severe 

than the full-blown manic episodes typical of bipolar 

I disorder). Additionally, people with SAD tend to 

have other mental disorders, such as attentiondeficit/hyperactivity disorder, an eating disorder, 

an anxiety disorder, or panic disorder. Learn more 

about these disorders by visiting the NIMH website 

at www.nimh.nih.gov/health. 

SAD sometimes runs in families. SAD is more common 

in people who have relatives with other mental 

illnesses, such as major depression or schizophrenia.

What causes SAD? 

Scientists do not fully understand what causes 

SAD. Research indicates that people with SAD 

may have reduced activity of the brain chemical 

(neurotransmitter) serotonin, which helps regulate 

mood. Research also suggests that sunlight 

controls the levels of molecules that help maintain 

normal serotonin levels, but in people with SAD, this 

regulation does not function properly, resulting in 

decreased serotonin levels in the winter. 

Other findings suggest that people with SAD 

produce too much melatonin—a hormone that is 

central for maintaining the normal sleep-wake cycle. 

Overproduction of melatonin can increase 

sleepiness. 

Both serotonin and melatonin help maintain the body’s 

daily rhythm that is tied to the seasonal night-day cycle. 

In people with SAD, the changes in serotonin and 

melatonin levels disrupt the normal daily rhythms. As 

a result, they can no longer adjust to the seasonal 

changes in day length, leading to sleep, mood, and 

behavior changes. 

Deficits in vitamin D may exacerbate these problems 

because vitamin D is believed to promote serotonin 

activity. In addition to vitamin D consumed with diet, 

the body produces vitamin D when exposed to 

sunlight on the skin. With less daylight in the winter, 

people with SAD may have lower vitamin D levels, 

which may further hinder serotonin activity. 

Negative thoughts and feelings about the winter and 

its associated limitations and stresses are common 

among people with SAD (as well as others). It is 

unclear whether these are “causes” or “effects” 

of the mood disorder, but they can be a useful 

focus of treatment.
How is SAD treated?

Treatments are available that can help many people 

with SAD. They fall into four main categories that may 

be used alone or in combination:

● Light therapy

● Psychotherapy

Talk to your health care provider about which treatment, 

or combination of treatments, is best for you. For tips 

for talking with your health care provider, refer to the 

NIMH fact sheet, Taking Control of Your Mental Health: 

Tips for Talking With Your Health Care Provider, at 

www.nimh.nih.gov/talkingtips. 

Light Therapy

Since the 1980s, light therapy has been a mainstay for 

the treatment of SAD. It aims to expose people with 

SAD to a bright light every day to make up for the 

diminished natural sunshine in the darker months. 

For this treatment, the person sits in front of a very 

bright light box (10,000 lux) every day for about 30 to 

45 minutes, usually first thing in the morning, from fall 

to spring. The light boxes, which are about 20 times 

brighter than ordinary indoor light, filter out the 

potentially damaging UV light, making this a safe 

treatment for most. However, people with certain eye 

diseases or people taking certain medications that 

increase sensitivity to sunlight may need to use 

alternative treatments or use light therapy under 

medical supervision. 

Psychotherapy or “Talk Therapy”

Cognitive behavioral therapy (CBT) is a type of talk 

therapy aimed at helping people learn how to cope 

with difficult situations; CBT also has been adapted 

for people with SAD (CBT-SAD). It is typically 

conducted in two weekly group sessions for 6 weeks 

and focuses on replacing negative thoughts related to 

the winter season (e.g., about the darkness of winter) 

with more positive thoughts. CBT-SAD also uses a 

process called behavioral activation, which helps 

individuals identify and schedule pleasant, engaging 

indoor or outdoor activities to combat the loss of 

interest they typically experience in the winter.

When researchers directly compared CBT with light 

therapy, both treatments were equally effective in 

improving SAD symptoms. Some symptoms seemed 

to get better a little faster with light therapy than with 

CBT. However, a long-term study that followed SAD 

patients for two winters found that the positive 

effects of CBT seemed to last longer over time. 

For more information on psychotherapies, visit 

www.nimh.nih.gov/psychotherapies. 

Medications 

Because SAD, like other types of depression, is 

associated with disturbances in serotonin activity, 

antidepressant medications called selective serotonin 

reuptake inhibitors (SSRIs) are also used to treat SAD

when symptoms occur. These agents can significantly 

enhance patients’ moods. Commonly used SSRIs 

include fluoxetine, citalopram, sertraline, paroxetine, 

and escitalopram.

The U.S. Food and Drug Administration (FDA) also has 

approved another type of antidepressant, bupropion, in 

an extended-release form, that can prevent recurrence 

of seasonal major depressive episodes when taken 

daily from the fall until the following early spring. 

All medications can have side effects. Talk to your doctor 

about the possible risk of using these medications for 

your condition. You may need to try several different 

antidepressant medications before finding one that 

improves your symptoms without causing problematic 

side effects. For basic information about SSRIs, 

bupropion, and other mental health medications,

visit www.nimh.nih.gov/medications. Also, visit the 

FDA website at www.fda.gov/drugsatfda for the 

most up-to-date information on medications, side 

effects, and warnings. 

Vitamin D

Because many people with SAD often have vitamin D 

deficiency, nutritional supplements of vitamin D may 

help improve their symptoms. However, studies testing 

whether vitamin D is effective in SAD treatment have 

produced mixed findings, with some results indicating 

that it is as effective as light therapy but others 

detecting no effect.

● Antidepressant medications

● Vitamin D
For More Information

MedlinePlus (National Library 

of Medicine)

https://medlineplus.gov 

(En español: https://medlineplus.

gov/spanish)

ClinicalTrials.gov

www.clinicaltrials.gov 

(En español: https://salud.nih.gov/

investigacion-clinica) 

Reprints

National Institute of Mental Health

Office of Science Policy, Planning, 

and Communications

Science Writing, Press, and 

Dissemination Branch

Phone: 1-866-615-6464

Email: nimhinfo@nih.gov

www.nimh.nih.gov

National Institute

of Mental Health

NIH Publication No. 20-MH-8138

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Social Media @NIMHgov

Can SAD be prevented?

Because the timing of the onset of winter patternSAD is so predictable, people with a history of 

SAD might benefit from starting the treatments 

mentioned above before the fall to help prevent or 

reduce the depression. To date, very few studies 

have investigated this question, and existing studies 

have found no convincing evidence that starting

light therapy or psychotherapy ahead of time could 

prevent the onset of depression. Only preventive 

treatment with the antidepressant bupropion 

prevented SAD in study participants, but it also 

had a higher risk of side effects. Therefore, people 

with SAD should discuss with their health care 

providers if they want to initiate treatment early 

to prevent depressive episodes.

Are there clinical trials studying SAD?

NIMH supports a wide range of research, including 

clinical trials that look at new ways to prevent, detect, 

or treat diseases and conditions—including SAD. 

Although individuals may benefit from being part of a 

clinical trial, participants should be aware that the 

primary purpose of a clinical trial is to gain new 

scientific knowledge so that others may be better 

helped in the future.

Researchers at NIMH and around the country conduct 

clinical trials with patients and healthy volunteers. 

Talk to your health care provider about clinical trials, 

their benefits and risks, and whether one is right for 

you. For more information about clinical research and 

how to find clinical trials being conducted around the 

country, visit www.nimh.nih.gov/clinicaltrials.

This publication is in the public 

domain and may be reproduced 

or copied without permission from 

NIMH. Citation of NIMH as a source 

is appreciated. To learn more about 

using NIMH publications, visit 

www.nimh.nih.gov/reprints.