Seasonal affective disorder (SAD): symptoms, causes, treatments

Steve Silvestro, MD - Contributor Avatar

Written by Alison Dalton 

Steve Silvestro, MD - Contributor Avatar

Written by Alison Dalton 

last updated: May 24, 2021

4 min read

If you live in a place with harsh winters, you may notice your mood is lower during those short, cold days each year. The sun seems to be in hiding for months at a time, it may rain or snow a lot, and you feel like you haven’t seen the light of day in ages. If this sounds familiar, you may experience something called seasonal affective disorder. 


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What is seasonal affective disorder?

Seasonal affective disorder (aptly known as SAD for short) is a type of depression with a seasonal pattern. It’s also called seasonal depression or winter depression, and it usually occurs during the late fall and winter months. There’s also a less-common type of SAD that happens during the spring and summer. Summer depression tends to have opposite symptoms from winter depression, such as lack of appetite, weight loss, and insomnia. This article talks about only the winter type of SAD, which is more common.

What are the signs and symptoms of SAD?

Seasonal depression is common, affecting 1–10% of Americans. Many of the signs and symptoms of SAD are almost like those of hibernation (Meesters, 2016):

  • Having less energy

  • Withdrawing from social activity

  • Sleeping more

  • Eating more

  • Craving carbohydrates

  • Gaining weight

  • Feelings of sadness or loss of interest in things you usually enjoy

  • Difficulty concentrating

You don’t need to have all of those symptoms to be diagnosed with SAD.

What causes seasonal affective disorder?

SAD is clearly linked with daytime light levels. In northern latitudes, where days are shorter during the fall and winter, there’s a higher rate of SAD than in southern latitudes, where days are longer (Meesters, 2016). Thanks to electrical lighting, we modern humans have lifestyles that are independent of dawn and dusk light signals. But our bodies are still sensitive to circadian rhythms, the 24-hour cycles that are part of the body’s internal clock (Wirz-Justice, 2018).

Exactly how circadian rhythms and lack of daylight affect your body and mood isn’t clear. But studies have shown that lack of exposure to natural light is linked with symptoms of depression. Lack of light also affects your levels of melatonin, a natural hormone involved in regulating sleep cycles, and cortisol, the “stress” hormone (Harb, 2015). For this reason, in architecture and other fields responsible for designing our modern environment, there’s a movement toward exposing people to more natural sunlight.

SAD may also be linked with drops in your level of the neurotransmitter serotonin caused by reduced sunlight (Meesters, 2016). Neurotransmitters, brain chemicals that transmit messages between neurons, or from neurons to muscles, can have a strong effect on your mood.

What are the risk factors for SAD?

You’re at higher risk to develop SAD if you (Galima, 2020):

  • Live in an area that has less light in winter (northern latitudes)

  • Have a family history of SAD

  • Are female

  • Are 18–30 years old

What are the treatments for SAD?

Some people with SAD move to areas with more sunlight. That’s not a practical solution for most people, but thankfully, there are some good treatments available. 

Light therapy (phototherapy)

The first-line treatment for SAD is light therapy, also called phototherapy (Meesters, 2016). One type of light therapy involves using a light box in the morning (not at night, as that could disturb your sleep patterns). Light boxes come in different sizes and types. You don’t look right at them—instead, they provide ambient light in your surroundings. They emit blue light, a type of light that’s found in morning sunlight and boosts your level of vitamin D. Typically, light boxes emit a light intensity of 10,000 lux (Munir, 2021).

Dawn simulators are another type of light therapy device. They mimic the amount of light that occurs first thing in the morning. The light intensity gradually increases during your last 30 minutes of sleep, before your regular alarm goes off. Light boxes and dawn simulators seem to work about equally well for seasonal depression (Danilenko, 2015).

Light therapy can be quite effective at treating SAD (Lam, 2020; Pjrek, 2020). One study found light therapy alone worked as well as an antidepressant like fluoxetine (see Important Safety Information) for treatment. The combination of both had the most consistent results (Lam, 2016). Having said that, most studies of light therapy have been limited in scope, so your own preferences should play an important part in treatment decisions by your healthcare provider and yourself (Nussbaumer-Streit, 2019).

Antidepressant medications

SAD is a form of depression, so the whole array of antidepressant medications can be considered for treating it. Because SAD is linked with serotonin levels, second-generation antidepressants, which target neurotransmitters, are often chosen. Among these medications, selective serotonin reuptake inhibitors (SSRIs) are a frequent choice (Melrose, 2015). One type of SSRI in particular, fluoxetine (brand name Prozac), is often used to treat SAD. Bupropion (brand name Wellbutrin; see Important Safety Information) is frequently used as well. These medications can have side effects, including nausea, headaches, insomnia, constipation, and dizziness.

Psychotherapy/cognitive behavioral therapy (talk therapy)

The evidence is mixed about the effectiveness of talk therapy for SAD. It may work better in combination with other forms of treatment (Galima, 2020).

What are alternative and complementary treatments for SAD?

A number of complementary or alternative treatments may help to relieve symptoms of SAD, including (Munir, 2021; Galima, 2020):

  • Vitamin D—Have your vitamin D level checked by your healthcare provider. If it’s low, supplements may be helpful.

  • Increased exercise—Exercise alone can work as well as antidepressants to relieve depression (Andersson, 2015).

  • Change in dietThe health of your gut biome (the bacteria that naturally occur in your digestive tract) is linked to your emotional health, so it may help to eat an improved diet, rich in vegetables, fruit, fiber, and healthy fats (Luna, 2015).

  • Increased exposure to natural light

  • Meditation

  • Sleep hygiene practicesThese can include going to bed and waking up at the same time every day, avoiding bright lights (like the screens of digital devices) before bedtime, and eliminating noise while you sleep.

How can you prevent getting SAD?

Because it occurs at about the same time every year, you can take steps to prevent SAD before it sets in. The same treatments that can work for treating SAD can also be used to prevent it.

Mood disorders like SAD can get worse over time. Don’t take chances with your mental health. If you’re experiencing symptoms of SAD, talk to your healthcare provider or a mental health professional.


If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

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Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

Current version

May 24, 2021

Written by

Alison Dalton

Fact checked by

Steve Silvestro, MD

About the medical reviewer

Dr. Steve Silvestro is a board-certified pediatrician and Associate Director, Clinical Content & Education at Ro.