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.

Key points

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.

The symptoms can be mild or severe and are as the same as depression, except with a seasonal pattern. If your symptoms are mild, try the self-care strategies listed below. If they are more severe, see your doctor.

SAD usually first begins between the ages of 20 to 30 but it can develop at any age. It affects four 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.

The Seasonal Pattern Affective Questionnaire is a useful screening tool to work out if you need to see your doctor.

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.

What are the causes of seasonal affective disorder?

The main theory is 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 their genes.

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
  • feel sad and you cry or feel like crying often
  • lose interest and pleasure in things you normally enjoy
  • feel despair, guilt or worthlessness
  • feel stressed or anxious
  • sleep and eat more or less than usual
  • don’t feel like seeing your friends and family.

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 depression is seasonal.

How is seasonal affective disorder treated?   

Your doctor will probably recommend either antidepressant medication or psychological therapy, or a combination of both. If your SAD is more severe, they may also recommend light therapy. As well, the treatment involves several self-care steps you can take (see below).

Light therapy

In light therapy, you sit by a special lamp called a light box for about 30 minutes to an hour each morning, 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 on light therapy is limited and while it may not work for everyone, it is worth a try because it causes few side effects.

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


Antidepressants are often prescribed to treat depression, and they may also sometimes be used to treat severe cases of SAD. They are best started at the beginning of winter before symptoms appear, and continued until spring.

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

 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.

 Read more about antidepressants.

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

  • spend time outside each day, especially early in the day
  • keep moving, as exercise boosts your mood
  • eat well, as healthy eating improves your energy and your outlook on life 
  • stay in touch with those closest to you
  • find fun things to do that don’t depend on good weather
  • get support (see below).

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
  • 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.

Learn more

Depression self-test The Low Down, NZ
Seasonal affective disorder (SAD) NHS Choices, UK, 2015
Seasonal affective disorder Patient Info, UK, 2016
How seasonal are you? Psychology Today, 2008
Tell Me Everything I Need to Know about Seasonal Affective Disorder (SAD) PsyCom, USA, 2021
Beating the Blues Online CBT programme, NZ
The Journal Online self-help programme, 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. The reliability and validity of the Seasonal Pattern Assessment Questionnaire: a comparison between patient groups J Affect Disord. 2004
  4. Seasonal affective disorder NHS Choices, UK, 2015
Credits: Health Navigator Editorial Team. Reviewed By: Dr Bev Haarhoff Last reviewed: 28 Sep 2017