Seasonal Affective Disorder Guide: Symptoms, Causes, Diagnosis, and Treatment

Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: September 2026

TL;DR: Seasonal affective disorder (SAD) is a type of depression tied to the changing of the seasons — it begins and ends at about the same times every year. For most people, symptoms start in the fall and run through the winter (low mood, oversleeping, carb cravings, low energy) and lift in spring; less often, it strikes in spring or summer with insomnia, poor appetite, and agitation. The leading theory links it to reduced sunlight disrupting your biological clock, serotonin, and melatonin. It is diagnosed through an evaluation that rules out other causes and is treated with light therapy (phototherapy), psychotherapy, and/or antidepressants — and self-care steps like getting outside within two hours of waking make a real difference.

Quick Answer

• What is SAD? A seasonal pattern of depression that starts and ends at roughly the same time each year — most often in fall/winter, less often in spring/summer.

• What does winter SAD look like? Oversleeping, carbohydrate cravings and weight gain, tiredness, and low energy.

• What does summer SAD look like? Insomnia, poor appetite, weight loss, agitation, anxiety, and irritability — the mirror image of winter SAD.

• Why does it happen? The leading contributors are a disrupted circadian rhythm from reduced sunlight, a drop in serotonin, and a seasonal melatonin imbalance.

• How is it treated? Light therapy within the first hour of waking, cognitive behavioral therapy, and antidepressants such as extended-release bupropion — often started before the season begins.

SAD follows two seasonal patterns: winter-onset (oversleeping, carb cravings, weight gain, low energy) and the less common summer-onset (insomnia, poor appetite, weight loss, agitation) — both repeat yearly and likely stem from a disrupted circadian rhythm, serotonin drop, and melatonin imbalance.

What Is Seasonal Affective Disorder?

Seasonal affective disorder is a type of depression that is related to changes in seasons — it begins and ends at about the same times every year.

If you are like most people with SAD, your symptoms start in the fall and continue into the winter months, sapping your energy and making you feel moody. These symptoms often resolve during the spring and summer. Less often, SAD causes depression in the spring or early summer that resolves during the fall or winter.

The important line to remember: this is more than the "winter blues." Don't brush off that yearly feeling as a seasonal funk you have to tough out alone — treatment exists, and taking steps keeps your mood and motivation steadier through the year.

What Are the Signs and Symptoms?

In most cases, symptoms appear during late fall or early winter and go away during the sunnier days of spring and summer. In either pattern, symptoms may start out mild and become more severe as the season progresses.

• Low mood — Feeling listless, sad, or down most of the day, nearly every day

• Lost interest — Losing interest in activities you once enjoyed

• Low energy — Feeling sluggish, with little drive

• Oversleeping — Problems with sleeping too much

• Carb cravings — Carbohydrate cravings, overeating, and weight gain

• Poor focus — Difficulty concentrating

• Hopelessness — Feeling hopeless, worthless, or guilty

• Dark thoughts — Thoughts of not wanting to live

The eight key signs of SAD are feeling down nearly every day, losing interest in activities, low energy, oversleeping, carb cravings and weight gain, poor concentration, hopelessness, and thoughts of not wanting to live — see a doctor if low mood lasts for days at a time.

How Does Winter SAD Differ from Summer SAD?

The two seasonal patterns look almost opposite — a useful way to tell them apart.

• Sleep — Fall/winter SAD brings oversleeping; spring/summer SAD brings trouble sleeping (insomnia).

• Appetite — Fall/winter SAD brings changes, especially craving high-carbohydrate foods; spring/summer SAD brings poor appetite.

• Weight — Fall/winter SAD brings weight gain; spring/summer SAD brings weight loss.

• Mood — Fall/winter SAD brings tiredness and low energy; spring/summer SAD brings agitation or anxiety and increased irritability.

A note on bipolar disorder: people who have bipolar disorder are at increased risk of SAD. In some, episodes of mania may be linked to a specific season — spring and summer can bring on mania or a milder form (hypomania), anxiety, agitation, and irritability, while fall and winter bring depression.

When Should You See a Doctor?

It is normal to have some days when you feel down. But if you feel down for days at a time and can't get motivated to do activities you normally enjoy, see your healthcare provider. This is especially important if your sleep patterns and appetite have changed, you turn to alcohol for comfort or relaxation, or you feel hopeless or think about suicide.

What Causes SAD?

The specific cause remains unknown, but three light-related factors appear to play a role.

• Your biological clock (circadian rhythm) — Reduced sunlight in fall and winter may disrupt your body's internal clock and lead to feelings of depression

• Serotonin levels — Serotonin is a brain chemical (neurotransmitter) that affects mood; reduced sunlight can cause a drop that may trigger depression

• Melatonin levels — The change in season can disrupt the balance of melatonin, which plays a role in sleep patterns and mood

Who Is at Higher Risk?

SAD is diagnosed more often in women than in men, and occurs more frequently in younger adults than in older adults.

• Family history — People with SAD often have blood relatives with SAD or another form of depression

• Major depression or bipolar disorder — Depression symptoms may worsen seasonally with one of these conditions

• Living far from the equator — More common far north or south, likely due to decreased winter sunlight and longer summer days

• Low vitamin D — Sunlight helps the skin produce vitamin D, which can boost serotonin activity; less sunlight plus insufficient dietary vitamin D may lower levels

What Are the Possible Complications?

Untreated, SAD can get worse — as with other types of depression — and lead to:

• Social withdrawal — Pulling away from friends and family

• School or work problems — Focus and motivation decline

• Substance abuse — Alcohol or drugs used for comfort

• Other mental health disorders — Such as anxiety or eating disorders

• Suicidal thoughts or behavior — The most serious risk of untreated depression

How Is SAD Diagnosed?

Even with a thorough evaluation, SAD can be hard to pin down, because other types of depression and mental health conditions cause similar symptoms. A full evaluation generally includes three parts.

• Physical exam — In-depth health questions; depression may be linked to an underlying physical health problem

• Lab tests — For example, a complete blood count (CBC) or a thyroid test to make sure it is functioning properly

• Psychological evaluation — Your provider asks about symptoms, thoughts, feelings, and behavior patterns; you may fill out a questionnaire

How Is SAD Treated?

Treatment may include light therapy, psychotherapy, and medications. One critical warning first: if you have bipolar disorder, tell your provider and mental health professional — light therapy or an antidepressant can potentially trigger a manic episode.

Light Therapy (Phototherapy)

Light therapy is one of the first-line treatments for fall-onset SAD. You sit a few feet from a special light box so that you're exposed to bright light within the first hour of waking up each day. It mimics natural outdoor light and appears to change brain chemicals linked to mood. It generally starts working in a few days to a few weeks and causes very few side effects. Research is limited, but it appears effective for most people in relieving SAD symptoms.

Before buying a light box, talk with your provider about the best one for you and how and when to use it, so you get a high-quality product that is safe and effective.

Psychotherapy (Talk Therapy)

Cognitive behavioral therapy (CBT) can help you learn healthy ways to cope with SAD — especially reducing avoidance behavior and scheduling meaningful activities — identify and change negative thoughts and behaviors that make you feel worse, manage stress, and build in healthy behaviors such as more physical activity and better sleep patterns.

Medications

Some people, especially those with severe symptoms, benefit from antidepressants. An extended-release version of bupropion (Wellbutrin XL, Aplenzin) may help prevent depressive episodes in people with a history of SAD, and other antidepressants are commonly used as well. Your provider may recommend starting an antidepressant before your symptoms typically begin each year and continuing past the time symptoms normally go away.

Keep in mind it may take several weeks to notice full benefits, and you may have to try different medications before finding one that works well with the fewest side effects.

SAD is diagnosed with a physical exam, lab tests (CBC, thyroid), and a psychological evaluation — treatment runs from first-line light therapy and cognitive behavioral therapy to antidepressants like bupropion; daily brightening, morning outdoor light, exercise, and a steady sleep schedule all help, and early treatment prevents worsening.

What Self-Care Steps Help?

Alongside your treatment plan, four daily habits make a measurable difference.

• Make your environment sunnier and brighter — Open blinds, trim tree branches that block sunlight, add skylights; sit closer to bright windows at home or the office

• Get outside — Walk, eat lunch in a park, sit on a bench in the sun; even on cold or cloudy days outdoor light helps — especially within two hours of getting up

• Exercise regularly — Physical activity relieves stress and anxiety (both can worsen SAD), and improved fitness lifts mood

• Normalize sleep patterns — Keep reliable wake and bed times daily; for fall-winter SAD, reduce or eliminate napping and oversleeping

What About Alternative Medicine?

Herbal remedies, supplements, and mind-body techniques are sometimes used to try to relieve depression symptoms, but it is not clear how effective they are for SAD. Herbal and dietary supplements are not monitored by the FDA the same way medications are, so you can't always be certain of what you're getting or whether it's safe. Some can interfere with prescription medications or cause dangerous interactions — talk to your provider or pharmacist before taking any supplements. When it comes to depression, alternative treatments are not a substitute for medical care.

How Can You Cope and Find Support?

Five practical habits help manage SAD day to day:

• Stick to your treatment plan — Follow the plan and attend therapy appointments when scheduled

• Take care of yourself — Sleep enough — but not too much, since SAD makes people feel like hibernating; exercise, eat well, and don't turn to alcohol or recreational drugs

• Practice stress management — Relaxation techniques such as yoga, tai chi, and meditation; unmanaged stress can feed depression and overeating

• Socialize — Make an effort to connect with people you enjoy — support, a shoulder to cry on, shared laughter

• Take a trip — Winter vacations in sunny, warm locations for winter SAD; cooler locations for summer SAD

How Should You Prepare for Your Appointment?

You may start with your healthcare provider or a mental health professional such as a psychiatrist or psychologist. Before the appointment, write down your symptoms (feeling down, lack of energy, excess sleeping, appetite changes), your depression patterns (when it starts, what makes it better or worse), any other mental or physical health problems, recent major stressors or life changes, and all medications, vitamins, herbs, and supplements with dosages.

Good questions to bring: whether your symptoms are likely SAD or something else; the best treatment options; whether a light box would help; whether you should see a psychiatrist or psychologist; whether medications will help; and whether a generic alternative exists. Expect your provider to ask when symptoms began, whether they're continuous or occasional, how they affect daily activities, what improves or worsens them, your other conditions and substances, and whether any blood relatives have SAD or another mental health condition.

Conclusion

Seasonal affective disorder has one thing most people overlook: it is predictable. It arrives and lifts at roughly the same time every year, which is both a burden and an advantage — because predictable means preventable. If you've noticed the pattern, the evidence-based toolkit is real: sit by a light box within the first hour of waking, get outside in the morning even on cloudy days, move your body, and protect your sleep schedule. Light therapy, CBT, and antidepressants — often started before the season turns — can keep the annual dip from ever taking hold. There is no reason to hibernate through it. If your mood sinks for days at a time, book the appointment now, not in January.

Next steps: explore more plain-language guidance on mental health, sleep health, and self-care and wellness to keep every season manageable.

This guide is for general information only and is not a substitute for professional medical advice. Always consult a qualified healthcare provider for diagnosis and treatment.

Frequently Asked Questions

What exactly is seasonal affective disorder?

SAD is a type of depression related to changes in seasons that begins and ends at about the same times every year — most often starting in fall and lasting through winter, resolving in spring and summer.

What are the symptoms of winter SAD?

The hallmark signs are oversleeping, appetite changes with a craving for high-carbohydrate foods, weight gain, and tiredness or low energy, along with general depression signs like persistent low mood and lost interest in activities.

Can you get SAD in the summer?

Yes — less commonly, SAD strikes in spring or summer. Summer depression looks like the opposite: trouble sleeping (insomnia), poor appetite, weight loss, agitation or anxiety, and increased irritability.

What causes SAD?

The specific cause is unknown, but reduced fall and winter sunlight appears to disrupt the body's biological clock (circadian rhythm), lower serotonin levels that affect mood, and upset the balance of melatonin, which regulates sleep and mood.

Who is most at risk?

SAD is diagnosed more often in women and younger adults. Risk also rises with a family history, having major depression or bipolar disorder, living far from the equator, and low vitamin D levels.

How is it diagnosed?

Through a thorough evaluation — a physical exam, lab tests such as a complete blood count or thyroid check, and a psychological evaluation — because other types of depression can look similar.

Does light therapy actually work?

Light therapy is a first-line treatment for fall-onset SAD: sitting a few feet from a special light box within the first hour of waking each day. It generally starts working in a few days to a few weeks with very few side effects and appears effective for most people.

Can it be prevented?

There's no known way to prevent SAD from developing, but early treatment — sometimes started before symptoms typically begin each year — can prevent it from getting worse and prevent complications.

References

• [1] Seasonal affective disorder — Symptoms & causes (updated December 14, 2021)

• [2] Seasonal affective disorder — Diagnosis & treatment (updated December 14, 2021)

What this guide is based on

Specialist-reviewed clinical guidance updated December 2021, alongside the DSM-5 diagnostic criteria for depression with a seasonal pattern, the National Institute of Mental Health SAD resource, the American Psychiatric Association and American Psychological Association patient guidance, the National Alliance on Mental Illness overview, the American Family Physician clinical review (2020), and peer-reviewed systematic reviews of complementary therapies for depression (BMJ Open, 2019).

Additional references consulted

• Specifiers for depressive disorders: With seasonal pattern. DSM-5, 5th ed., American Psychiatric Association, 2013

• Seasonal affective disorder. National Institute of Mental Health

• Seasonal affective disorder (SAD). American Psychiatric Association

• Seasonal affective disorder: More than the winter blues. American Psychological Association

• Major depressive disorder with a seasonal pattern. National Alliance on Mental Illness

• Galima SV, et al. Seasonal affective disorder: Common questions and answers. American Family Physician, 2020;102:668

• Haller H, et al. Complementary therapies for clinical depression: An overview of systematic reviews. BMJ Open, 2019

• Rosenthal SJ, et al. Seasonal effects on bipolar disorder: A closer look. Neuroscience and Biobehavioral Reviews, 2020