Seasonal Affective Disorder (SAD): When the Seasons Affect Mental Health / By Dr. Bob Lee, DO, MS, MBA.

Seasonal affective disorder is a form of depression marked by a predictable seasonal pattern. The name is almost painfully appropriate. Seasonal affective disorder is commonly abbreviated as SAD, and for many people, that acronym captures the experience exactly. For most individuals, symptoms begin in the fall or early winter, intensify during the darkest months, and then ease with the return of longer days in spring. Less commonly, some people experience the opposite pattern, with symptoms emerging in late spring or summer and resolving in the fall.

Although many people casually refer to this as the “winter blues,” SAD is not a mild or purely psychological reaction to cold weather. It is a clinically defined subtype of major depressive disorder, associated with measurable biological changes and meaningful impairment in daily functioning.

Recognizing the Pattern
Many patients recognize seasonal affective disorder long before they ever hear the term.

One graduate student told me that every November, without fail, her motivation collapsed. “I start sleeping through alarms, my emails pile up, and I feel guilty all the time – but I don’t feel lazy. I feel stuck.” By April, she felt like herself again, almost bewildered that winter had affected her so deeply. Another patient, a middle-aged professional, described what he called his “January fog.” “I stop exercising, stop calling friends, and I’m convinced I’m bad at my job – even though nothing has changed.” He had assumed this was a character flaw for years, not a treatable condition.

That predictability – the way symptoms reliably return with the seasons and remit when daylight increases – is one of the most important clues that seasonal affective disorder may be present.

Seasonal Affective Disorder in the DSM-5
In the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), seasonal affective disorder is not listed as a standalone diagnosis. Instead, it is diagnosed as major depressive disorder, recurrent, with seasonal pattern, or, in some cases, bipolar disorder with seasonal pattern.

The DSM-5 specifies several criteria for the seasonal pattern specifier:

A regular temporal relationship between the onset of depressive episodes and a particular time of year.

Full remission, or a switch to mania or hypomania, at a characteristic time of year.

At least two consecutive years in which this pattern is observed, without nonseasonal depressive episodes during that period.

Seasonal episodes outnumber nonseasonal episodes over the individual’s lifetime.

I often explain to patients that this diagnosis is less about severity and more about reliability. If depression arrives and leaves on a calendar schedule, that information matters – and it can guide treatment in powerful ways.

Who Is Affected?

Seasonal affective disorder affects approximately 5% of adults in the United States, with another 10% to 20% experiencing milder seasonal mood changes that still interfere with daily life. It is diagnosed more frequently in women than men and typically begins in young adulthood, though it can appear earlier. Geography also plays a role: people who live farther from the equator, where winter daylight is limited, are at higher risk. One patient who relocated from Southern California to the Pacific Northwest described feeling blindsided by her first winter. “I kept waiting to adjust,” she told me. “Instead, I just kept getting sadder.” Her symptoms resolved almost completely the following spring. Family history of depression or bipolar disorder also increases risk, as does a personal history of mood disorders.

What SAD Feels Like Day to Day
Because seasonal affective disorder is a subtype of major depressive disorder, its symptoms overlap with depression more broadly, but often with a distinctive seasonal signature.

Common symptoms include:

Persistent low mood or sadness

Loss of interest or pleasure in activities

Low energy and physical heaviness

Difficulty concentrating or thinking clearly

Increased sleep and difficulty waking

Increased appetite, especially carbohydrate cravings

Weight gain

Social withdrawal

Feelings of hopelessness, guilt, or worthlessness

Many patients describe not just emotional pain, but a bodily sense of slowing down. One person told me, “It feels like my brain switches to power-saving mode.” Cognitive symptoms are especially common. People often report brain fog, forgetfulness, or trouble finding words – symptoms that can be frightening if they don’t realize depression can affect cognition.

Winter-Onset vs. Summer-Onset SAD
Winter-onset SAD is by far the most common form and is associated with hypersomnia, increased appetite, weight gain, and low energy.

Summer-onset SAD, which is much rarer, tends to present with insomnia, agitation, anxiety, irritability, decreased appetite, and weight loss. In these cases, heat and circadian disruption may play a larger role than light deprivation alone.

Why Light Matters So Much
The strongest evidence suggests that seasonal affective disorder is driven primarily by reduced exposure to natural light. Sunlight regulates the brain’s circadian rhythm, the internal clock that controls sleep, hormone release, alertness, and mood. When daylight shortens, this rhythm can become misaligned. Sunlight also affects serotonin, a neurotransmitter involved in mood regulation, and melatonin, a hormone that promotes sleep. In winter, serotonin activity may decrease while melatonin levels rise, leading to fatigue, low mood, and excessive sleepiness. I often explain to patients that their brains are responding appropriately to darkness – but in a modern world that expects year-round productivity, that response becomes a problem.

Treatment That Works
Seasonal affective disorder is highly treatable, and many patients respond more quickly and robustly than they do with nonseasonal depression.

Light Therapy
Light therapy is often the first-line treatment for winter-onset SAD. It involves daily exposure to bright artificial light, typically 10,000 lux, which mimics natural sunlight. Most people use a light box for 15 to 30 minutes each morning, ideally before 10 a.m. The light is positioned off to the side, allowing people to read or eat while using it. One patient described light therapy as “giving my brain a fake sunrise.” Within two weeks, her energy and motivation began to return.

Clinical studies show improvement in 50% to 80% of patients. Side effects are usually mild and transient, though people with bipolar disorder or certain eye conditions should use light therapy under medical guidance.

Antidepressant Medications
Antidepressants are another effective option. The most commonly prescribed class is selective serotonin reuptake inhibitors (SSRIs), which increase serotonin availability in the brain. Examples include Prozac (fluoxetine), Zoloft (sertraline), and Lexapro (escitalopram). Wellbutrin (bupropion), an antidepressant that affects dopamine and norepinephrine, is also commonly used and may be started preventively in the fall for individuals with a clear seasonal pattern.

Psychotherapy
Cognitive behavioral therapy (CBT) is particularly effective for SAD. It helps patients identify seasonal negative thought patterns, reduce avoidance, and maintain meaningful routines during winter months. One patient told me that CBT helped her stop “waiting for spring to live again.”

Supporting Recovery Outside the Clinic
Lifestyle strategies can significantly enhance treatment:

Spending time outdoors during daylight hours

Exercising regularly

Maintaining consistent sleep schedules

Increasing indoor lighting

Staying socially connected, even when motivation is low

Isolation often worsens seasonal depression. Small, intentional connections can be protective, even when energy is limited.

When to Seek Help
Seasonal mood changes are common. But if symptoms last weeks, impair functioning, or recur at the same time each year, professional evaluation is warranted. Mental health diagnoses always require a professional evaluation by a physician – such as a psychiatrist, a mental health specialist. Any thoughts of death or suicide require immediate attention. In the United States, the Suicide and Crisis Lifeline (988) is available 24 hours a day.

Closing Thoughts
Seasonal affective disorder may live up to its acronym, but it is not something people need to endure in silence. SAD is real, biologically influenced, and highly responsive to treatment. With recognition, planning, and the right interventions, winter does not have to mean months of suffering. For many patients, understanding the pattern is the first step toward reclaiming the season – and themselves.