Seasonal affective disorder

Also known as SAD

Seasonal affective disorder (SAD) is a type of depression that occurs over autumn and winter and improves during spring and summer. However, you don’t just have to endure these darker months – there are things you can do to manage this condition.

On this page, you can find the following information:

Key points

  1. Seasonal affective disorder (SAD) appears to be linked to light, as it occurs more commonly in places furthest away from the equator. 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.
  2. 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 doctor.
  3. SAD usually first begins between the ages of 20 to 30 but it can develop at any age. It affects 4 times as many women as men. Those most at risk are female, young, live far from the equator and have family histories of depression, bipolar disorder or SAD.
  4. In New Zealand, you are most likely to experience SAD from about May to September, but because the winter months in the northern hemisphere are the opposite to ours, some resources mention different months.

(NHS 24, UK 2022)

What are the causes of seasonal affective disorder?

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.

What are the symptoms of seasonal affective disorder?

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.

How is seasonal affective disorder diagnosed?

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.

How is seasonal affective disorder treated?   

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 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.

How can I care for myself if I have seasonal affective disorder?

What support is available for someone with seasonal affective disorder?

Join a support group 
Find a counsellor or therapist 
Get help online at or 
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).

How can I prevent seasonal affective disorder?

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.

Learn more

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


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

Reviewed by

Kris Garstang is consulting clinical psychologist at Life Mind Psychology. She has practiced as a registered clinical psychologist for over twenty years and is a fellow of the New Zealand College of Clinical Psychologists. She has expertise in different evidence based psychological therapies including cognitive behavioural therapy, acceptance and commitment therapy and dialectical behaviour therapy. Areas of interest include primary mental health, e-therapies, mental health leadership and workplace wellbeing.
Credits: Health Navigator Editorial Team. Reviewed By: Kris Garstang, Clinical Psychologist, Life Mind Psychology Last reviewed: 10 May 2022