Also called: SAD · Seasonal depression · Seasonal mood disorder
Important: This page is general information, not medical advice. It does not recommend or prescribe any treatment. Always consult your doctor or pharmacist before starting, stopping or changing any medicine.
About Seasonal Affective Disorder
Seasonal affective disorder (SAD) is a type of depression that comes and goes with the seasons. It usually starts in the late fall and early winter and goes away during the spring and summer. Some people do have episodes of depression that start in the spring or summer, but that is a lot less common. Symptoms of SAD may include:
- Sadness
- Gloomy outlook
- Feeling hopeless, worthless, and irritable
- Loss of interest or pleasure in activities you used to enjoy
- Low energy
- Difficulty sleeping or oversleeping
- Carbohydrate cravings and weight gain
- Thoughts of death or suicide
SAD is more common in women, young people, and those who live far from the equator. You are also more likely to have SAD if you or your family members have depression.
The exact causes of SAD are unknown. Researchers have found that people with SAD may have an imbalance of serotonin, a brain chemical that affects your mood. Their bodies also make too much melatonin, a hormone that regulates sleep, and not enough vitamin D.
The main treatment for SAD is light therapy. The idea behind light therapy is to replace the sunshine that you miss during the fall and winter months. You sit in front of a light therapy box every morning to get daily exposure to bright, artificial light. But some people with SAD do not respond to light therapy alone. Antidepressant medicines and talk therapy can reduce SAD symptoms, either alone or combined with light therapy.
It sits within Mental Health and Behavior.
The lead U.S. institute for this subject is the National Institute of Mental Health.
When to speak to someone. Reading about a topic cannot tell you whether it applies to you. Speak to a doctor or pharmacist if symptoms are severe, sudden, getting worse, or simply not going away — and seek emergency care immediately for chest pain, breathing difficulty, sudden weakness or confusion, or a serious allergic reaction.
Research on Seasonal Affective Disorder
37 studies areregistered for this condition on ClinicalTrials.gov, the U.S. National Library of Medicine's public registry. A selection is below — the links go straight to the registry entry, not to a summary of ours.
What a registered study does and does not mean. Registration means a study exists and has been declared publicly. It says nothing about whether the treatment being tested works, is safe, or is available to you. Many studies find no benefit — that is what research is for. Never seek out an experimental treatment on the strength of a registry entry alone.
Research currently under way
- Virtual Reality Digital Therapeutics for Seasonal Affective DisorderAnglia Ruskin University
- Cohort of Patients Suffering From Major Depressive Episode With Evaluation of Sleep, Circadian Rhythms and Psychiatric DisordersAssistance Publique - Hôpitaux de Paris
Research already completed
- Optimizing Long-Term Outcomes for Winter Depression With CBT-SAD and Light TherapyUniversity of Vermont
- Vitamin D Supplementation and Effects on Mood in Emergency Medicine ResidentsCorewell Health South
- Health Consequences of Wintering in the French Southern and Antarctic TerritoriesCentre Hospitalier Universitaire de la Réunion
- Cognitive-behavioral Therapy vs. Light Therapy for Preventing SAD RecurrenceUniversity of Vermont
- Investigation of Seasonal Variations of Brain Structure and Connectivity in SADSunnybrook Health Sciences Centre
- Infrared Photomodulation Therapy for Seasonal Affective DisorderProofPilot
Study data from ClinicalTrials.gov, a service of the U.S. National Library of Medicine. Retrieved 2026-07-30. Registry entries are supplied by study sponsors and investigators; ClinicalTrials.gov does not verify their scientific validity. PocketsInfo is not affiliated with, and not endorsed by, the NLM or the NIH.
Where to read more
Rather than paraphrase, we point you to the primary sources. Every link below is to a government health agency, a national institute or a recognised medical body — grouped by what you are trying to find out.
Learn More
- Feeling SAD?: Identifying and Treating Seasonal Affective DisorderNational Institutes of Health
- PsychotherapiesNational Institute of Mental Health
- Seasonal Affective DisorderNational Institute of Mental Health
- Seasonal Affective Disorder (SAD)Nemours Foundation
- Seasonal Affective Disorder (SAD)Mayo Foundation for Medical Education and Research
- Seasonal Affective Disorder (SAD): More than the Winter BluesNational Institute of Mental Health
- Seasonal Affective Disorder Sufferers Have More than Just Winter BluesAmerican Psychological Association
- Seasonal affective disorder treatment: Choosing a light boxMayo Foundation for Medical Education and Research
Genetics
- Seasonal affective disorder: MedlinePlus GeneticsNational Library of Medicine
Clinical Trials
- ClinicalTrials.gov: Seasonal Affective DisorderNational Institutes of Health
Medical subject headings
Clinicians and researchers index this subject under Seasonal Affective Disorder. These are the terms to use when searching medical literature.
This page is built from the MedlinePlus health topic record for Seasonal Affective Disorder, a service of the U.S. National Library of Medicine (NLM), National Institutes of Health. Information is from MedlinePlus.gov. PocketsInfo is not affiliated with, and is not endorsed by, the NLM or the NIH. Retrieved 30 July 2026.