Seasonal affective disorder

Also known as SAD

Key points about seasonal affective disorder

  • Seasonal affective disorder (SAD) is a type of depression occurring in autumn and winter and improving in spring and summer.
  • It appears to be linked to light,.
  • While it’s normal to feel a bit less energetic and to eat and sleep a little more in winter, if your mood or habits change a lot, you may have SAD.
  • The symptoms can be mild or severe and are as the same as depression, but with a seasonal pattern. If your symptoms are mild, try the self-care strategies listed below. If they are more severe, see your healthcare provider.
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Video: What is Seasonal Affective Disorder? (SAD)

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(NHS 24, UK 2022)

Researchers think that a lack of sunlight might stop a part of the brain called the hypothalamus from working properly. This affects:

  • The production of melatonin. Melatonin is a hormone that makes you feel sleepy, and in people with SAD, your body may produce it in higher than normal levels.
  • The production of serotonin. Serotonin is a hormone that affects your mood, appetite and sleep. A lack of sunlight may lead to lower serotonin levels, which is linked to feelings of depression.
  • Your body's internal clock (circadian rhythm). Your body uses sunlight to time various important functions, such as when you wake up. Lower light levels during the winter may disrupt your body clock and lead to symptoms of SAD.

It's possible that some people are more vulnerable to SAD because of genes inherited from their whānau/family.

You may have SAD if during the winter months you:

  • Have a low mood most of the time. You may experience this as feeling sad, low, flat or numb.
  • Lose interest and pleasure in things you normally enjoy.
  • Feel guilt or worthlessness.
  • Sleep and eat more or less than usual.
  • Don’t feel like seeing your friends and family.
  • Have trouble concentrating.
  • Notice that you move and think more slowly than normal.
  • Think about dying.

If you have symptoms of SAD, it’s important to see your doctor before they get worse. Your doctor will ask you about your mood, sleep, eating, thoughts you’ve been having and whether you’ve had depression before. They may also recommend some blood tests. Because it is common for people who have had depression to get it again, it can take a few years for you and your doctor to work out if your symptoms are seasonal.

Your doctor will probably recommend antidepressant medication, psychological therapy or a combination of both. If your symptoms are more severe, they may also recommend light therapy. 

Psychological therapy

Cognitive Behavioural Therapy (CBT) is a type of talking therapy that helps you to use activities and thoughts to improve your mood. Research shows that CBT is an effective treatment for SAD. Ask your doctor to refer you to a psychologist or counsellor who is trained in the use of this effective therapy. Most New Zealand trained clinical psychologists are trained in CBT. You can search for a clinical psychologist(external link) near you.

Otherwise, you can use an online therapy programme like Beating the Blues or Just a Thought to beat SAD.

Light therapy

In light therapy, you sit by a special lamp called a light box for about 30 minutes to an hour each morning, shortly after waking, so that you're exposed to bright light. Light therapy mimics natural outdoor light and appears to cause a change in brain chemicals linked to mood.

The recommended light boxes have filters that remove harmful ultraviolet (UV) rays, so there's no risk of skin or eye damage for most people. Research shows that light therapy is an effective treatment for SAD. 

When light therapy has been found to help, most people notice an improvement in their symptoms within a week or so. Ask your doctor about whether light therapy is an option for you and how to get a light box.

Another type of light therapy is called dawn stimulation. It involves a special kind of light that gradually brightens your room, mimicking the light at sunrise. This has also been found to work well for SAD.


Antidepressants are often prescribed to treat depression, and they may also sometimes be used to treat severe cases of SAD. 

There are many different types of antidepressants, but the selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine, citalopram, escitalopram or paroxetine are preferred for treating SAD. They increase the level of the hormone serotonin in your brain, which can help lift your mood.

If you're prescribed antidepressants, you should be aware that:

  • it can take up to 4 to 6 weeks for the medication to take full effect
  • you may have to try different medications before you find one that works well for you and has the fewest side effects
  • you should take the medication as prescribed and continue taking it until advised to gradually stop by your doctor
  • some antidepressants have side effects and may interact with other types of medication you're taking.

Once you know that your symptoms of depression follow a seasonal pattern, you can use medication to prevent further bouts in winter. Research shows that the medication Bupropion is the most effective for preventing SAD before it kicks in during the winter months. Read more about antidepressants.

Read more tips for managing SAD.

In the summer months, develop habits that you can carry over even in winter that make sure you spend time outside in daylight each day, particularly in the first half of the day. This could be to exercise outside when you get up in the morning, walk part of the way to work, go for a walk at lunchtime or have lunch outside wherever possible. On the weekend, keep up a regular outdoor activity, such as sport, gardening, going for a bike ride with a friend or playing in the park with your children. Bupropion is the only medication found to reliably prevent SAD.

Join a support group(external link) 
Find a counsellor or therapist(external link) 
Get help online at link) or link) 
Phone a helpline:

  • Lifeline 0800 543 354 or (09) 5222 999 within Auckland
  • Free counselling 1737 
  • Suicide Crisis helpline 0508 828 865 (0508 TAUTOKO)
  • Healthline 0800 611 116
  • Samaritans – 0800 726 666
  • Depression helpline – 0800 111 757 or free text 4202 (to talk to a trained counsellor about how you are feeling or to ask any questions).

Depression self-test(external link) The Low Down, NZ
Seasonal affective disorder (SAD)(external link) NHS Choices, UK, 2015
Seasonal affective disorder(external link) Patient Info, UK, 2016
Tell me everything I need to know about seasonal affective disorder (SAD)(external link) PsyCom, US, 2021
Beating the blues(external link) Online CBT programme, NZ
Small Steps(external link) Online resources for helping you to manage stress, calm your mind and lift your mood, NZ


  1. Seasonal affective disorder(external link) Patient Info, UK, 2016
  2. Seasonal affective disorder – an overview of assessment and treatment approaches(external link) Depression Research and Treatment, 2015 
  3. Seasonal affective disorder(external link) NHS Choices, UK, 2015
  4. Galima SV, Vogel SR, Kowalski AW. Seasonal Affective Disorder – common questions and answers(external link) Am Fam Phys. 2020 Dec 1;102(11):668-772

Diagnosing seasonal affective disorder

It can take several years to diagnose seasonal affective disorder (SAD). However, as it is considered a type of recurring major depression with a seasonal pattern, this does not affect treatment.

According to the Diagnostic and Statistical Manual of Mental Disorders DSM-V, the criteria for Major Depressive Disorder with a seasonal pattern include having depression that begins and ends during a specific season every year (with full remittance during other seasons) for at least two years and having more seasons of depression than seasons without depression over a lifetime. Seasonal pattern disorders occur most frequently in winter although they can also occur in summer.

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

  • Bipolar I and ll disorders (all patients with autumn- or winter-onset depression should be screened for spring or summer hypomania or mania symptoms. An estimated 20% of people with SAD may present with a bipolar disorder).
  • Dysthymic disorder.
  • Cyclothymic disorder.
  • Premenstrual dysphoric disorder (associated with bloating and breast tenderness with onset during the latter part of the luteal phase of the menstrual cycle and remission of symptoms during the follicular phase).
  • Chronic fatigue syndrome.
  • Substance misuse.
  • Alcohol misuse.

The Seasonal Pattern Assessment Questionnaire(external link)  is a commonly used assessment tool for SAD. While it’s not sensitive enough for diagnosis on its own, it is seen as valid as a screening tool. Scoring information(external link) is available but note that there is an error – the 4th bullet point says “A GSS of 11 or higher and a score on Q.11 of moderate or greater is indicative of SAD” when it should say “A GSS of 11 or higher and a score on Q.17 of moderate or greater is indicative of SAD” as it mentions Q17 in the previous bullet point.

SSRIs are particularly effective for women with depression.

Clinical resources

  1. Melrose, S. Seasonal affective disorder: An overview of assessment and treatment approaches. Depression Research and Treatment, link)
  2. Seasonal affective disorder(external link) Patient Info Professional Reference, UK, 2016
  3. Mersch PP, Vastenburg NC, Meesters Y, et al. The reliability and validity of the Seasonal Pattern Assessment Questionnaire: a comparison between patient groups(external link) J Affect Disord. 2004 Jun;80(2-3):209-19.
  4. Mc Mahon B, Andersen SB, Madsen MK, Hjordt LV, Hageman I, Dam H. Seasonal difference in brain serotonin transporter binding predicts symptom severity in patients with seasonal affective disorder(external link) Brain. 2016;139(5):1605-1614. 

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Credits: Healthify editorial team. Healthify is brought to you by Health Navigator Charitable Trust.

Reviewed by: Kris Garstang, Clinical Psychologist, Life Mind Psychology

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