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Mental health Condition

Seasonal affective disorder (SAD)

Seasonal affective disorder (SAD) is a type of depression that follows a seasonal pattern — most commonly occurring in autumn and winter when daylight hours shorten, then lifting in spring. It affects around 2 million people in the UK and a further 10% experience a milder form. It is a real, recognised condition — not just "winter blues" — and responds well to several specific treatments.

What is Seasonal affective disorder (SAD)?

SAD is classified as a subtype of recurrent depressive disorder with a seasonal pattern. For most people, symptoms begin in October or November, worsen through December and January, and lift naturally in spring. A smaller number experience summer SAD — a less common pattern where symptoms occur in the warmer months.

The cause is not fully understood, but the leading theory involves reduced sunlight affecting the hypothalamus, leading to disrupted production of melatonin (the sleep hormone) and serotonin (a neurotransmitter that affects mood, appetite and sleep). Circadian rhythm disruption also plays a role.

SAD is more than simply disliking winter. When it is clinical SAD, it involves the full symptom picture of depression, recurring predictably each year and significantly affecting quality of life.

Signs and symptoms

SAD symptoms typically mirror those of depression but with some distinctive features:

  • Persistent low mood, hopelessness and tearfulness during winter months
  • Loss of interest or pleasure in activities
  • Increased sleep (hypersomnia) — a distinctive feature of SAD compared to other depression
  • Increased appetite, particularly for carbohydrates — often leading to weight gain
  • Low energy and feeling lethargic
  • Difficulty concentrating
  • Social withdrawal
  • Irritability
  • Symptoms lifting reliably in spring or with increased light exposure

How therapy can help

SAD has several treatment options, often used in combination:

  • Light therapy — sitting in front of a specialist light therapy lamp (10,000 lux) for 30 minutes each morning. This is often the first-line treatment and produces significant improvement for many people within 1–2 weeks
  • CBT adapted for SAD — addresses the behavioural withdrawal and negative thinking patterns specific to seasonal depression
  • Antidepressants — SSRIs are recommended by NICE for SAD and are effective, though many people prefer to avoid year-round medication for a seasonal condition
  • Dawn simulation — a gentler alternative to bright light therapy that involves gradually brightening light while you sleep
  • Increased outdoor time and exercise — getting outside during daylight hours, even on cloudy days, and maintaining regular physical activity through winter

Talking therapy — CBT, counselling or mindfulness-based approaches — can help address both the acute seasonal episodes and the underlying vulnerability to SAD.

Seeking help

If you experience significant mood changes that predictably worsen each winter and improve in spring, and this has happened for at least two consecutive years, it is worth speaking to a GP or therapist. SAD is well recognised and there are effective treatments.

A light therapy lamp can be purchased without a prescription and is a reasonable first step to try. Your GP can assess whether antidepressants are appropriate and can refer to psychological therapies.

Therapies that may help with Seasonal affective disorder (SAD)

We don't currently have any therapies mapped to this condition.

Frequently asked questions

How do I know if I have SAD or just dislike winter?

SAD is a clinical condition involving the full symptom picture of depression recurring predictably each winter and lifting in spring. It is distinct from simply finding winter difficult or preferring summer. If low mood, increased sleep, carbohydrate cravings and withdrawal are significantly affecting your life each winter and have done for at least two years, SAD is worth discussing with a GP.

Do light therapy lamps really work for SAD?

Yes — light therapy has good evidence for SAD and is recommended by NICE as a treatment option. Around 50–80% of people with SAD respond to light therapy. The key is using a lamp with a minimum 10,000 lux rating for around 30 minutes each morning, ideally within an hour of waking.

Can SAD occur in summer?

Yes, though it is much less common. Summer SAD typically involves insomnia, reduced appetite, weight loss, agitation and anxiety — a different profile from the more common winter SAD. It is thought to be triggered by heat and humidity rather than light changes.

Is SAD just depression?

SAD is a subtype of recurrent depression with a seasonal specifier. The key distinguishing features are the predictable seasonal pattern, the tendency towards increased rather than decreased sleep, and increased appetite particularly for carbohydrates. These features mean the treatment approach is somewhat distinct from non-seasonal depression.

Will SAD get worse each year?

Not necessarily. With appropriate treatment and management — including light therapy, maintaining activity through winter, and therapy — many people reduce the severity of seasonal episodes significantly. Understanding and preparing for the seasonal pattern, rather than being caught off guard each year, makes a meaningful difference.