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Seasonal affective disorder

Medical Professionals

Professional Reference articles are designed for health professionals to use. They are written by UK doctors and based on research evidence, UK and European Guidelines. You may find the Seasonal affective disorder article more useful, or one of our other health articles.

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What is seasonal affective disorder?1

Seasonal affective disorder (SAD) is a seasonal pattern of recurrent major depressive episodes that most commonly occurs during autumn or winter and remits in spring. In some cases, SAD may occur in the summer with remission in the autumn-winter.2 It can be very disabling for patients, some of whom may require hospitalisation for SAD at some point.

How common is seasonal affective disorder? (Epidemiology)

  • The prevalence of SAD ranges from 1.5% to 9%, depending on latitude.1

  • Possible risk factors include family history, female sex, living at a more northern latitude, and young adulthood (18 to 30 years of age).3

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Seasonal affective disorder symptoms (Presentation)

Patients may develop the following symptoms in a step-wise fashion, beginning in September and culminating with depression and anxiety in December. SAD symptoms persist until springtime in April.

  • Difficulty waking.

  • Decreased energy.

  • Lethargy.

  • Carbohydrate craving.

  • Increased appetite.

  • Increased sleep.

  • Weight gain.

  • Difficulty concentrating.

  • Decreased libido.

  • Withdrawal from family and friends.

  • Depression/anxiety/irritability.

Other symptoms include:

  • Family problems.

  • Tearfulness.

  • Physical symptoms - eg, headache, palpitations and generalised aches and pains.

Differential diagnosis

The patient should be assessed for other psychological conditions, including:

Many of these disorders do not have a seasonal pattern. The seasonality of symptoms may be determined by asking the patient to record symptoms in a diary.

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TFTs and urine and blood tests for illicit substances and alcohol will help to rule out some of the above conditions.


The diagnosis of SAD is based on:

  • Depression cycles on a regular basis during autumn/winter.

  • Full remission of symptoms in spring/summer.

  • Seasonal symptoms for at least two consecutive years.

  • Atypical features, which may or may not be present.

During the psychological examination, it is also important to assess:

  • Suicidal ideation.

  • Abnormal mechanisms of coping - eg, social isolation, alcohol use.

Associated disorders4

Seasonal affective disorder treatment3 5

The most current National Institute for Health and Care Excellence (NICE) guidelines for depression state that depression in SAD patients should be managed in the same way as non-seasonal depression. NICE recommend advising people with winter depression that follows a seasonal pattern and who wish to try light therapy in preference to antidepressant medication or psychological treatment that the evidence for the efficacy of light therapy is uncertain.6

Cognitive behavioural therapy (CBT) and antidepressant medications have all been found to help to induce remission of SAD symptoms during winter months.

Lifestyle interventions, such as increasing exercise and exposure to natural light, are also recommended.

If seasonal affective disorder recurs, long-term treatment or preventive intervention is typically indicated, and bupropion appears to have the strongest evidence supporting long-term use. Continuing light therapy or other antidepressants is likely beneficial, although evidence is inconclusive. Evidence is also inconclusive for psychotherapy and vitamin D supplementation.


  • Give information about the disorder and self-help groups.

  • Simple advice should include the following:

    • Spend more time out of doors.

    • Work in bright conditions.

    • Exercise outside regularly.

    • Eat a healthy diet.

Light therapy, or phototherapy

Light therapy, or phototherapy, may be carried out using various devices such as a light box, LED screen and a light room; however, the light box is the most commonly used. Light therapy is associated with poor compliance.

A Cochrane review found that the evidence on light therapy as preventive treatment for people with a history of SAD is limited. The review concluded that, given that comparative evidence for light therapy versus other preventive options is limited, the decision for or against initiating preventive treatment of SAD and the treatment selected should be strongly based on patient preferences.1

General instructions for light therapy

  • Sit for 30-60 minutes daily in an area with bright light. The light is much stronger than regular light sources, of the order of 2,500-10,000 lux (the greater the lux, the less time of exposure required).

  • Light therapy helps approximately two thirds of patients .

  • Although randomised trials are difficult to perform, attempts at comparisons of light therapy show that light therapy is as effective as drug therapy .

  • Light therapy can take several weeks to produce any effect; if it takes longer than six weeks, extra help should be sought. However, it is not available on the NHS, although some hospitals may have facilities available on site.

  • Common side-effects include headache, irritability and fatigue.

  • Dawn simulators are also available.

  • Despite all of these, more lux is available from natural sunlight.

Relative contra-indications for light therapy

  • Retinal disease.

  • Macular degeneration.

  • Current use of photosensitising medicines (such as some antihypertensives, antibiotics and oncology drugs).

Compliance with light therapy is difficult and relapses occur rapidly if treatment is discontinued.


A Cochrane review found that the evidence for the effectiveness of second generation antidepressants is limited to one small trial of fluoxetine compared with placebo showing a non-significant effect in favour of fluoxetine, and two small trials comparing fluoxetine against light therapy suggesting equivalence between the two interventions.7

Psychological - CBT

A Cochrane review found that the evidence on psychological therapies to prevent the onset of a new depressive episode in people with a history of SAD is inconclusive. It was concluded that, given that there is no comparative evidence for psychological therapy versus other preventive options, the decision for or against initiating preventive treatment of SAD and the treatment selected should be strongly based on patient preferences.8

Further reading and references

  • Munir S, Abbas M; Seasonal Depressive Disorder. StatPearls, Jan 2023.
  • Meesters Y, Gordijn MC; Seasonal affective disorder, winter type: current insights and treatment options. Psychol Res Behav Manag. 2016 Nov 30;9:317-327. doi: 10.2147/PRBM.S114906. eCollection 2016.
  1. Nussbaumer-Streit B, Forneris CA, Morgan LC, et al; Light therapy for preventing seasonal affective disorder. Cochrane Database Syst Rev. 2019 Mar 18;3(3):CD011269. doi: 10.1002/14651858.CD011269.pub3.
  2. Fonte A, Coutinho B; Seasonal sensitivity and psychiatric morbidity: study about seasonal affective disorder. BMC Psychiatry. 2021 Jun 29;21(1):317. doi: 10.1186/s12888-021-03313-z.
  3. Galima SV, Vogel SR, Kowalski AW; Seasonal Affective Disorder: Common Questions and Answers. Am Fam Physician. 2020 Dec 1;102(11):668-672.
  4. Levitan RD; The chronobiology and neurobiology of winter seasonal affective disorder. Dialogues Clin Neurosci. 2007;9(3):315-24.
  5. Yildiz M, Batmaz S, Songur E, et al; State of the art psychopharmacological treatment options in seasonal affective disorder. Psychiatr Danub. 2016 Mar;28(1):25-9.
  6. Depression in adults: treatment and management; NICE guideline (June 2022)
  7. Nussbaumer-Streit B, Thaler K, Chapman A, et al; Second-generation antidepressants for treatment of seasonal affective disorder. Cochrane Database Syst Rev. 2021 Mar 4;3(3):CD008591. doi: 10.1002/14651858.CD008591.pub3.
  8. Forneris CA, Nussbaumer-Streit B, Morgan LC, et al; Psychological therapies for preventing seasonal affective disorder. Cochrane Database Syst Rev. 2019 May 24;5(5):CD011270. doi: 10.1002/14651858.CD011270.pub3.

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The information on this page is written and peer reviewed by qualified clinicians.

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