What is seasonal affective disorder (SAD)?

Seasonal affective disorder, usually shortened to SAD, is a type of depression that follows a seasonal pattern. For most people in the UK it begins in late autumn, deepens through the darkest weeks of December and January, and lifts as daylight returns in spring. Depression that comes on in winter and goes away in summer is how the NHS describes it, and it’s still widely known as “winter depression”.

It isn’t the same thing as having a flat week because the evenings have drawn in. SAD is a recognised depressive illness in which the change of season is the trigger. Year after year, the symptoms are the ones that define depression, and they return at roughly the same point in the year.

Why so many people in the UK are affected

During winter, the NHS is clear that the exact cause is unknown, but that SAD is thought to be linked to the reduction in daylight. Less light appears to disturb two things: the brain chemicals that regulate mood, including serotonin and melatonin, and the body clock that governs sleep and waking (the circadian rhythm). Shorter, greyer days keep the body clock out of step with the working week, and the effect on mood follows.

Geography matters. SADA, the UK’s Seasonal Affective Disorder Association, notes that the further you live from the equator, the higher the likelihood of SAD, and that countries such as the United Kingdom, where cloud cover and rain are frequent, tend to report higher rates than places with brighter winters. Family history of depression, long-term stress and traumatic experiences are also listed as risk factors, and surveys consistently suggest women are affected more often than men.

In practical terms: if your mood dips every October and recovers every April, you aren’t imagining the pattern, and you aren’t alone in it.

Winter SAD and summer SAD

Winter-pattern SAD is by far the most common form. A minority of people experience the reverse, with depression arriving in spring or summer instead. At the start of spring or summer, the NHS also notes that some people have a spell of feeling more energetic than usual. Both patterns are treatable.

Symptoms of seasonal affective disorder

Main symptoms of SAD, as the NHS lists them:

• Persistent low mood
• A lack of interest or pleasure in things you would normally enjoy
• Feeling guilty, hopeless or worthless
• Feeling restless or irritable
• Difficulty concentrating
• Being hungrier than usual and eating more
• Being more tired and sleeping more than usual
• Thoughts of suicide or self-harm

That last point is the one that matters most. If you are having thoughts of suicide or self-harm, treat it as urgent: contact your GP, call NHS 111, call Samaritans free on 116 123, or text SHOUT to 85258. There’s no need to wait for an appointment to get help today.

The symptoms that make winter SAD distinctive

Two of those symptoms stand out because they run opposite to what many people picture when they think of depression. Rather than losing their appetite and lying awake, people with winter SAD often sleep more, feel heavy and sluggish on waking, and eat more, frequently craving starchy, comforting food. When a clinician sees that cluster alongside a reliable seasonal pattern, SAD moves up the list of explanations.

SAD and depression: what is actually different

Both are depression. What differs is the pattern, the physical symptoms and the timing of treatment.

If you already know that you live with depression, SAD isn’t a separate illness that erases it. Many people have a baseline low mood that worsens sharply in winter, and that pattern is worth describing clearly to whoever is treating you.

Treatments for SAD in the UK

Three main medical treatments for SAD are listed by the NHS: talking therapies, light therapy and antidepressants. Alongside those sits the self-care advice that genuinely shifts symptoms for many people.

1. Talking therapy, especially CBT

Cognitive behavioural therapy is the talking therapy most often recommended for SAD. Winter SAD suits CBT particularly well because the problem is predictable: a good therapist will help you examine the thoughts and behaviours that keep low mood running through the darker months, and then build a plan you can put in place before the season arrives rather than after it has taken hold. If you’re weighing up who to see, our guide to cognitive behavioural therapy explains how the approach works in practice.

You don’t need a GP referral to start. Anyone aged 18 or over, and 16 or over in some areas, can self-refer to NHS talking therapies directly. Waiting times and available therapies vary a great deal between areas, which is one reason many people choose to see a therapist privately and start within days.

2. Light therapy (SAD lamps and light boxes)

Light therapy means sitting beside a bright, UV-free lamp at roughly the strength of a bright spring morning for a set time each day. The NHS position is worth quoting precisely: it isn’t usually available on the NHS because there isn’t yet enough evidence to say for certain whether it works, but many people find it helps their symptoms. The NHS advises speaking to a GP before trying it, because it may not be suitable if you have certain eye conditions or take medication that makes you more sensitive to light.

If you do buy a lamp, the NHS suggests it should be bright enough (10,000 lux is the standard), UV-free, and carry a UKCA or CE mark, and that you follow the manufacturer’s instructions. In practice most people use it in the morning for a fixed block of time, placed to the side of the face rather than stared into, while working or reading.

3. Antidepressants

A GP may prescribe an SSRI such as sertraline or fluoxetine if symptoms are moderate to severe, and some people with a clear seasonal pattern begin medication earlier in the autumn so that it’s working by the time symptoms would normally start. Medication decisions should be made with a doctor. How they are used, what side effects to expect and how to stop them safely are set out on the NHS page on SSRI antidepressants.

4. The self-care that the NHS recommends

For SAD, the daily habits the NHS advises are unglamorous and effective: get outside in natural daylight every day, take regular exercise, stay in contact with friends and family, keep up your usual activities, and go to bed and wake at the same time each day. It also advises not drinking too much alcohol or using illegal drugs, and not using phones or screens right before bed. Poor sleep and alcohol both amplify low mood, and both are easy to lean on during a British winter. Our guide to the link between sleep and mental health explains why the routine matters as much as the lamp.

5. Vitamin D: useful, but not a treatment for SAD

During the autumn and winter, the NHS recommends that adults in the UK consider a daily supplement of 10 micrograms of vitamin D, when sunlight is too weak for the skin to make it. That advice exists because of bone and muscle health rather than mood: it’s a sensible winter baseline, not a cure for depression. If you are taking it hoping to lift your mood by itself, treat it as one small part of the plan rather than the plan.

Comparing the options

SAD and the rest of the year: plan ahead, not too late

For anyone with a history of winter SAD, the single most useful thing to do is to treat autumn as the start of treatment rather than the diagnosis. Concretely:

• Book therapy in September or October, before waiting lists lengthen and before your energy for arranging anything drops away.
• Set your light routine now and fix it to something you already do every morning, so it survives the mornings you least feel like it.
• Protect your sleep window. Late nights in November pay for themselves in mood by January. Keep the wake time fixed even when the sleep time slips.
• Get outside during daylight hours, even when it’s grey: overcast daylight is still many times brighter than indoor lighting.
• Keep the commitments you enjoy, at exactly the point when withdrawing feels easier. Isolation is what low mood uses to keep hold of you.
• Write down how you felt last winter, including roughly when it started and what helped, and take it to your GP or therapist. Two years of that record is what the NHS says is needed for a seasonal diagnosis.
• Have the crisis numbers in your phone already rather than searching for them at 2am.

Where to go next if you want to talk to someone

You can see a GP, self-refer to NHS talking therapies, or start therapy privately. If you would rather not navigate that alone, we can help you work out what you need first and then match you with a registered therapist: start with the short therapy needs assessment, or go straight to connect with a psychotherapist and tell us what has been happening. Sessions are typically £50–£120 depending on the therapist and location. Our UK therapy pricing guide sets out the ranges, and our guide to choosing the right therapist covers what to ask before you commit. If you are still weighing up the NHS and private routes, that comparison breaks down waiting times, cost and choice.

Winter will still be winter. But the pattern is predictable, and predictable problems respond well to planning, which is the whole reason SAD tends to respond so well to therapy that starts early.