Seasonal affective disorder (SAD): symptoms, causes and treatment

The symptoms, causes, and treatment options for SAD, or winter depression.

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Page medically reviewed by Dr Rupesh Adimulam (MBBS, MRCPsych), Consultant Neuropsychiatrist at Priory Hospial Chelmsford in January 2022.

What is SAD?

Seasonal affective disorder (SAD), sometimes known as ‘winter depression’, is a type of depression and formally recognised mental health condition.

The symptoms of SAD, including persistent low moods, a lack of energy, and poor concentration, are typically experienced in a seasonal pattern, emerging in the winter months when people are exposed to less natural daylight, and decreasing in spring and summer.

The majority of people with SAD live in the northern and southern hemispheres (places that experience longer hours of darkness during winter). SAD is much less common in people living near the equator, where daylight hours are reliably long and bright.

What are the warning signs of SAD?

seasonal affective disorder symptoms and causesThe signs and symptoms of SAD will typically occur at a similar time every year, usually during the autumn and winter months when there's less sunlight. They include:

  • Feeling low and depressed
  • Feeling excessively tired during the day and needing to sleep for longer
  • Having difficulty getting up in the morning, despite having more sleep
  • Social withdrawal and loss of pleasure and interests
  • Loss of libido
  • Feelings of irritability, tension, stress and anxiety
  • Carbohydrate cravings, waking up in the night to eat, and weight gain
  • Feelings of despair, guilt and worthlessness
  • Suicidal thoughts

If the signs you're experiencing align with that of seasonal depression, you can make one or two changes to your daily routine that will help you cope with SAD. 

Why does the weather affect my mood?

The exact cause of SAD can differ depending on each person, just as the causes of all types of depression do. It may also be a combination of things that contribute to the likelihood of you developing SAD. However, there are a few distinct factors that research shows are linked to SAD.

Poor sleep patterns

Your body’s internal clock, known as your circadian rhythm, uses sunlight as a guide for when you should wake up or go to sleep. With the lower levels of sunlight during winter, your body’s biological clock may become disrupted, leading to symptoms of SAD.

Serotonin and melatonin levels

It's also believed that SAD may be related to the activity of the hypothalamus (a portion of the brain that links the nervous system to the endocrine system). The hypothalamus produces varying levels of melatonin (the ‘sleep hormone’), according to the amount of sunlight we're exposed to, which can affect our sleep and mood patterns. Similarly, less sunlight can lead to a drop in how much serotonin we produce. Serotonin is a brain chemical that affects our mood, so any reduction can lead to symptoms of depression.

Why do people get SAD?

Some additional factors might make someone more vulnerable to developing SAD. These include:

  • Age - the risk of being affected by SAD decreases with age, with the highest rate of cases among those aged 18 to 30
  • Gender - women are more likely to experience SAD than men
  • Location - rates of SAD are higher in parts of the world with less sunlight and longer winter nights. In general, the further you go from the equator the more at risk you are of SAD. If you work outside, allowing you to get more sunlight, this might also decrease your risk of developing SAD
  • Family history - genetics can play a role in causing SAD. If you have a family history of SAD, or other types of depression, then you may be at higher risk of developing the condition yourself

If you already suffer from depression, SAD can increase the existing depression symptoms that you experience throughout the rest of the year. If you find there’s a link between you feeling depressed and the nights drawing in during winter, it’s important to understand that SAD is a treatable condition. It’s crucial that you seek help as early as possible, so you can start your journey towards recovery.

SAD treatment

To be diagnosed with SAD, your symptoms of depression will tend to resurface on an annual basis, coinciding with the winter months and lessen when spring returns. For people who are suffering with SAD, know that there are treatment options available that can reduce your symptoms and and help you to live your life the way you want to, no matter the time of year.

Common SAD treatments include:

Light therapy using lightboxes

Light therapy can be a very effective treatment for SAD, with most people seeing an improvement of their symptoms within the first week. Lightboxes are powerful lamps that replicate natural light. High quality lightboxes are recommended as they allow people to spend a short amount of time (30 minutes) using them. However, some people prefer ‘lower lux’ lightboxes, as these can be positioned on the corner of their desks at work. Light therapy imitates sunlight, which helps to trigger the release of serotonin in the brain, helping to improve your mood. Some people also find dawn simulators to be an effective treatment of SAD. Essentially these are light-based alarm clocks that have a timer that you adjust before you go to sleep. The light in a dawn simulator mimics the morning sunrise, aiding your body clock and ensuring a healthier sleep pattern. Guidance for buying lightboxes, including any risks involved, can be found on the seasonal affective disorder and depression (SADA) website.

Talking therapies

Cognitive behavioural therapy (CBT) is also known to be helpful in alleviating winter depression and possibly preventing it from re-emerging in the future. CBT identifies the link between our thoughts, behaviour and mood. Therapy involves helping people to become more aware of their negative thought patterns, which can lead to unhealthy behaviours and emotions. It also helps people to adjust any underlying beliefs they may have, which could be maintaining their unhealthy thinking patterns and behaviours. Teaching people to challenge their negative thoughts and modify their behaviour, can lead to a significant improvement in mood.


Selective serotonin reuptake inhibitors (SSRIs), a type of antidepressant, can be an effective treatment for SAD, particularly when they're taken alongside therapy. To be most effective in treating SAD, SSRIs such as fluoxetine or sertraline, should be started in the autumn and discontinued in the spring. Antidepressants can be prescribed by your GP or a psychiatrist – make sure you speak to your doctor or read the leaflet to understand any side effects or risks associated with them.

Private medical insurance

We are a registered and approved provider for all of the UK's leading private medical insurers. All of the services we offer at Priory can be funded through private medical insurance. This includes:

  • Mental health treatment
  • Addiction treatment
  • Eating disorder treatment

All clients will have access to our highly skilled and accredited clinicians, many of whom are published experts in their fields of treatment. Whatever your requirements, we're committed to working with you to get your life back on track.

Registered and approved provider

We are a registered and approved provider for all of the UK's leading private medical insurers.

Seasonal affective disorder (SAD) treatment near me

We have SAD treatment centres located throughout the country, ensuring that you can access the support you need in a location that's convenient for you. To find your nearest SAD treatment centre, please use the search form below.

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