Seasonal Affective Disorder (SAD)

Seasonal Affective Disorder (SAD) is a form of depression that occurs at specific times of the year, most commonly during the fall and winter months when daylight hours are shorter.

People with SAD have mood shifts and symptoms similar to depression, such as persistent sadness, low energy, changes in appetite, and sleep problems. The difference is timing. These symptoms tend to occur around the same season each year, then improve as the seasons change.

In rare cases, individuals can have a spring/summer pattern of SAD (sometimes called “summer depression”), though winter-onset SAD is far more common.

SAD is not rare. An estimated 5% of the U.S. population experiences it. In the U.K., the figure is roughly 3%. Women are around four times more likely than men to be affected.

Note: This article is for informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of a qualified health provider with any questions about your mental health.

Signs of SAD

Because SAD is essentially a type of depression with a seasonal pattern, its symptoms mirror those of major depressive disorder, occurring cyclically during a particular season.

Common signs and symptoms may include:

• Feeling depressed or sad most of the day, almost every day during the episode
• Low energy, fatigue, or feeling “sluggish” and unmotivated
• Sleeping much more than usual (oversleeping) and struggling to get up in the morning
• Changes in appetite (often craving carbohydrates) and weight gain
• Loss of interest in activities you usually enjoy (including socializing; reduced libido is also common)
• Feelings of hopelessness or worthlessness
• Irritability, or feeling anxious and agitated
• Difficulty concentrating or making decisions
• In severe cases, frequent thoughts of death or suicide (if you experience these, seek help immediately)

Not everyone with SAD experiences all these symptoms, and the severity can range from mild “winter blues” to more debilitating depression.

Winter-pattern SAD may more often involve oversleeping, overeating, and low energy, whereas someone with summer-pattern SAD might have more insomnia, reduced appetite, and weight loss.

The risks grow if SAD goes unmanaged. Individuals might withdraw from friends and family, losing important social support. They may also turn to alcohol or other substances to cope, which can worsen their condition.

In the most serious cases, untreated SAD can lead to suicidal thoughts or self-harming behaviors.

How Is SAD Diagnosed?

SAD is not a separate diagnosis in the DSM-5, the diagnostic manual used by clinicians. Instead, clinicians add the specifier “with seasonal pattern” to a diagnosis of recurrent major depressive disorder or, less often, bipolar disorder. The criteria are deliberately strict (American Psychiatric Association, 2013).

The specifier applies when all of these are met:

• Timing: Depressive episodes begin at a regular time of year and are not explained by a seasonal stressor, such as seasonal unemployment.
• Remission: Episodes fully remit at a characteristic time of year. In bipolar disorder, mood may shift to mania or hypomania instead.
• Two years: The pattern has appeared across at least two consecutive years, with no non-seasonal episodes in that period.
• Lifetime pattern: Across the person’s life, seasonal episodes substantially outnumber non-seasonal ones.

A single low winter proves nothing on its own. The criteria separate a genuine recurring pattern from ordinary seasonal changes in mood.

Personal experiences of SAD

Despair, Fatigue, and “Hibernation”

Individuals who experience SAD speak of feeling sad, hopeless, or even in despair for months on end.

One woman shared that as autumn turns to winter, “a veil of darkness sits heavily over me until spring.” She described a heavy, depressive shroud that won’t lift.

Experts note that “The winter version of SAD is often compared to hibernation. People lack energy, sleep more than usual, crave sweets and starchy food, and gain weight. They may withdraw socially and have a hard time concentrating.”

Daily life with SAD can feel like walking through molasses. One person lamented, “I just can’t stay awake and the thought of having to go out, stay awake, make conversation… I just can’t do it.”

Withdrawal and Dread

When energy and mood are low, people tend to withdraw from others. A normally outgoing person might suddenly cancel plans. They may avoid gatherings or become irritable with loved ones.

“If SAD could be reduced to some simple math equation it would look something like social life + winter = impossible,” one person shared.

There is often anticipatory anxiety, even during summer or good periods, about the return of dark days. “I find myself dreading the change in seasons and the return of SAD even when I’m doing well,” one sufferer shared. It shows how the cycle looms over the whole year.

What Causes SAD?

The precise cause of SAD is not fully understood. It is closely tied to the seasonal reduction in sunlight.

One major factor is a disruption of the body’s circadian rhythm (internal biological clock) due to the late sunrise and early sunset in winter.

With less sunlight to regulate our waking and sleeping, the brain’s schedule shifts. This can trigger feelings of lethargy and depression.

Reduced light exposure is also believed to cause an imbalance in brain chemicals. In particular, serotonin, a neurotransmitter that affects mood, may be less active during darker months, which could contribute to depression.

Newer brain research is testing this serotonin story. A 2026 meta-analysis pooled seven imaging studies of healthy volunteers scanned in summer and winter.

It found no overall seasonal change in the serotonin transporter, the protein that clears serotonin from the gap between neurons (Pak, 2026).

A winter rise appeared only in studies that compared different people. Studies that rescanned the same people found none. This suggests a winter rise may mark vulnerability to SAD rather than a rhythm every brain follows.

Other chemicals may matter too. A small 2026 scan study of 14 people with SAD and 14 matched controls found lower GABA, the brain’s main calming neurotransmitter, in the hippocampus (Spurny-Dworak et al., 2026).

The sample is small, so the result needs replication.

Melatonin may play a role too. This sleep-related hormone is released for longer on long winter nights. Some researchers think this prolonged signal adds to fatigue and oversleeping. Direct evidence for this idea is weaker than for the body-clock explanation.

How Light Shapes the Body Clock

Light reaches the body clock through its own dedicated route. Berson et al. (2002) recorded from rat retinas and found ganglion cells that respond to light directly, even when input from the rods and cones is blocked.

The phase-shift hypothesis proposes a chain of events:

• Detection: Those retinal cells report overall brightness rather than visual detail.
• Signaling: They pass the message to the suprachiasmatic nucleus (SCN), the brain’s master clock in the hypothalamus.
• Delay: Late, dim winter mornings delay the clock. The body’s internal night then runs later than the clock time at which a person must be awake.

Research supports the idea. In one study of people with winter depression, depression ratings correlated with circadian phase, a measure of the clock’s timing (Lewy et al., 2006). Treatment may work best when it is timed to the person’s own clock.

The picture is incomplete. Not everyone with SAD shows a delayed clock, so researchers think more than one mechanism may be involved.

What are the risk factors?

Beyond these biological mechanisms, certain risk factors make a person more susceptible to SAD:

• People living in high latitudes (farther from the equator) are at greater risk, presumably because they experience much shorter, darker days in winter.
• Having a close relative with depression or having another mood disorder (like major depression or bipolar disorder) yourself can also increase risk.
• Women are about four times more likely to develop SAD than men.
• Personality may play a role. In a 2014 study of 101 adults, people who screened positive for SAD or milder winter blues scored higher on neuroticism. This trait is the tendency to feel negative emotions (Oginska & Oginska-Bruchal, 2014).

Does Latitude Affect SAD Risk?

Researchers have long linked SAD to distance from the equator. In 1990, Rosen and colleagues mailed a seasonal-symptoms questionnaire to residents of four U.S. areas, from New Hampshire in the north to Florida in the south.

Winter SAD and milder winter symptoms were significantly more common at the northern sites. Summer SAD showed no latitude pattern (Rosen et al., 1990).

A 2025 meta-analysis pooled 24 studies and nearly 33,000 people.

It found that winter SAD (5.01% of people) and milder winter symptoms short of full SAD (9.37%) rise with latitude, while summer SAD (0.57%) does not (Kim et al., 2025).

Not every study agrees. A large U.S. survey of adults found no link between depression and latitude, season, or sunlight exposure. Its authors suggested the seasonal modifier might deserve to be dropped (Traffanstedt et al., 2016).

Critics replied that one cross-sectional survey is poorly suited to a pattern that needs the same people tracked across seasons (Young, 2017).

The latitude effect looks real for winter SAD. It is still debated.

Treatments and Self-Help Approaches (Informational Only)

Managing SAD often combines professional treatments with self-help strategies. The approaches below are for information only. Always consult a healthcare provider before deciding on any treatment.

Light Therapy

Light therapy involves sitting near a special light box that mimics outdoor light.

A session lasts about 20-30 minutes each day. It is thought to cause a chemical change in the brain that lifts mood. SAD symptoms may improve within a week or two of regular use.

It is generally considered low-risk and is a first-line treatment for SAD. However, consultation is essential. Experts advise speaking with a healthcare provider before starting light therapy, especially for people with conditions like bipolar disorder (risk of triggering mania) or eye problems.

Most protocols use a light box of about 10,000 lux, many times brighter than ordinary indoor lighting.

Sessions are usually first thing in the morning. Some protocols run up to an hour.

Morning light is usually advised because it may shift a delayed body clock earlier. Evening light can help too.

In a placebo-controlled trial of 96 people with SAD, 61% responded to morning light and 50% to evening light, by one strict response measure. Only 32% responded to an inactive placebo (Eastman et al., 1998).

“For both seasonal and nonseasonal depression, the effectiveness of light therapy is approximately the same as antidepressant medications or popular forms of psychotherapy such as cognitive behavioral therapy,”

Dr. Richard S. Schwartz of Harvard Medical School.

How Well Does Light Therapy Work?

A 2005 meta-analysis pooled randomized trials of light therapy for mood disorders. For SAD, bright light across eight studies had an effect size of 0.84, comparable to most antidepressant trials (Golden et al., 2005). Larger effect sizes mean a bigger benefit.

A later meta-analysis of 19 placebo-controlled trials found a smaller but significant benefit. Bright light beat placebo on depression scores and response rates. The trials were small and varied in quality (Pjrek et al., 2020).

Dawn simulation also helps. It is a lamp that brightens gradually before waking, like a sunrise.

In a six-week trial of 95 adults with SAD, it produced higher remission and response rates than both bright light and a dim red placebo light (Avery et al., 2001). Bright light did not differ significantly from placebo in that trial.

Color may matter too. A network meta-analysis of 17 trials (773 patients) ranked white light most effective, then green, blue, and red (Wan et al., 2025). Green and blue light were tested in few trials, so the ranking is tentative.

Medication (SSRIs)

Antidepressant medications are another common treatment, particularly for more severe SAD.

Selective serotonin reuptake inhibitors (SSRIs) are often used. They work by increasing serotonin levels in the brain to help improve mood.

Doctors sometimes recommend starting an SSRI in early fall before symptoms begin and continuing it through spring.

Antidepressants can take several weeks (often 4–6 weeks) to reach full effect. They should be taken as prescribed under medical supervision.

Like any medication, SSRIs may have side effects. A healthcare professional will weigh the potential benefits and risks for each individual. No specific medication is universally “best” for SAD, so treatment is tailored to the person.

What Does the Research Say About Antidepressants?

Starting early can prevent episodes. In three placebo-controlled trials of 1,042 people with a history of winter SAD, patients began the antidepressant bupropion XL in autumn, while still well. It acts on noradrenaline and dopamine rather than serotonin.

Recurrence rates were 13% to 19% on bupropion XL, against 21% to 31% on placebo. That is a 44% relative risk reduction (Modell et al., 2005).

Medication also holds up against light therapy. In the Can-SAD trial, 96 patients received eight weeks of either bright light or fluoxetine, an SSRI.

Response rates were identical at 67%. Light worked faster in the first week, and fluoxetine caused more of some side effects, such as agitation and palpitations (Lam et al., 2006).

Psychotherapy

Talk therapy, especially Cognitive Behavioral Therapy (CBT), is a widely used non-medical approach.

CBT helps individuals identify and adjust unhelpful thought patterns and behaviors that contribute to depression.

Mental health professionals might use CBT to help someone with SAD cope with winter’s challenges. It can, for example, reframe unhelpful thoughts about darker months. Another target is “hibernation” thinking, which discourages activity and social contact.

Behavioral activation is another tool. It means deliberately re-engaging with activities and people to counter withdrawal and encourage healthy activities.

Research has shown that CBT can effectively treat SAD.

In a trial of 177 adults, six weeks of CBT tailored for SAD matched light therapy for an acute episode (Rohan et al., 2015). CBT may have longer-lasting benefits than light therapy alone.

By the second winter, depression had returned in about 27% of the CBT group, versus about 46% of the light therapy group (Rohan et al., 2016).

Light therapy users did not have to keep using it.

As SAD researcher Dr. Kelly Rohan explains, CBT is more of a preventive treatment. “Once SAD sufferers learn its basic skills it has enduring impact, giving the person a sense of control over their symptoms”.

Professional therapy may be used on its own or in combination with light therapy and/or medication, depending on individual needs.

Lifestyle and Self-Care (General Information)

In addition to professional care, certain lifestyle changes may support your well-being during the fall and winter months. These self-help approaches are general measures that many experts recommend:

• Maximize exposure to natural daylight: Take a brief walk at lunchtime or sit near a window. Daylight helps realign your body’s internal clock (circadian rhythm), and even cloudy days provide more light than indoor lighting.
• Regular physical exercise: Staying active may boost mood and energy, especially outdoors. Even moderate activities like walking, cycling, or yoga can improve sleep and reduce stress.
• Maintaining routines: Keep consistent sleep, wake, and meal times, and avoid oversleeping. A stable routine helps regulate your circadian rhythm, which can steady your mood and give a sense of control.
• Social support and activities: Join social activities and seek support from friends or family. Telling loved ones about SAD and your winter mood changes can help them support you. Group activities, clubs, or volunteering add structure and positive interactions.

Discuss these options with a healthcare professional to determine suitability.

Do you need mental health help?

USA

Call or text 988 to reach the 988 Suicide & Crisis Lifeline for support from a trained counselor. If you or a loved one are in immediate danger: https://988lifeline.org/

988

UK

Contact the Samaritans for support and assistance from a trained counselor: https://www.samaritans.org/; email jo@samaritans.org .

Available 24 hours a day, 365 days a year (this number is FREE to call):

116-123

Rethink Mental Illness: rethink.org

0300 5000 927

Further Reading

• Depression: How effective are antidepressants? Institute for Quality and Efficiency in Health Care, National Center for Biotechnology Information, U.S. National Library of Medicine. January 12, 2017.
• Gupta, A., Sharma, P. K., Garg, V. K., Singh, A. K., & Mondal, S. C. (2013). Role of serotonin in seasonal affective disorder. Eur Rev Med Pharmacol Sci, 17(1), 49-55.
• Levitt, A. J., & Lam, R. W. (Eds.). (1999). Canadian consensus guidelines for the treatment of seasonal affective disorder. Clinical & Academic Pub.
• Eastman, C. I., Young, M. A., Fogg, L. F., Liu, L., & Meaden, P. M. (1998). Bright light treatment of winter depression: a placebo-controlled trial. Archives of General Psychiatry, 55(10), 883-889.

References

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Eastman, C. I., Young, M. A., Fogg, L. F., Liu, L., & Meaden, P. M. (1998). Bright light treatment of winter depression: A placebo-controlled trial. Archives of General Psychiatry, 55(10), 883–889. https://doi.org/10.1001/archpsyc.55.10.883

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