Winter depression is real, and the treatment everybody recommends for it rests on thinner evidence than its reputation implies. Both of those statements are worth holding at once, because the usual coverage picks one.
The starting point is that this is not a separate illness. It is depression that recurs at a particular time of year.
It is a pattern, not a condition
In the current diagnostic manuals, seasonal affective disorder is a seasonal pattern specifier attached to major depressive disorder or bipolar disorder rather than a diagnosis of its own.
That sounds like bookkeeping and it has a practical consequence: the episodes have to meet the criteria for depression. Sustained low mood or loss of pleasure over at least two weeks, with genuine impairment. Preferring summer does not qualify. Losing three months of every year does.
Prevalence estimates commonly range between roughly 1.5% and 9%, varying with latitude. That gradient is the most persuasive evidence that light is genuinely involved, because very little else about a population changes so reliably with how far north it lives.
The winter version looks wrong
One reason people discount this in themselves is that it does not resemble their idea of depression.
The winter presentation tends to be atypical: sleeping considerably more rather than less, eating more rather than less, craving carbohydrates, gaining weight, and a heavy leaden fatigue rather than agitation.
So the internal argument writes itself. I am sleeping ten hours and eating constantly, that is not depression, that is just winter and being lazy. Our guide to depression subtypes covers how much presentations vary and why it changes what gets offered.
A schematic contrast of typical and atypical presentations as described in this article. Not measured data.
The two columns barely overlap, which is why somebody with the left-hand pattern can conclude with total confidence that they are not depressed.
What the light therapy evidence actually says
This is the part where the honest answer is less satisfying than the popular one.
Meta-analytic work has reported meaningful benefits from bright light treatment in seasonal affective disorder. [golden-2005-light] Reviewers looking at the field since have repeatedly flagged the same problem: the trials tend to be small, and the quality of evidence is low. A Cochrane review examining light therapy for preventing seasonal depression found the evidence base thin enough that firm conclusions were not available. [nussbaumer-2019-cochrane]
And NICE says this out loud. Its guidance advises that people with winter depression who want to try light therapy in preference to antidepressants or psychological treatment should be told that the evidence for its efficacy is uncertain. [nice-ng222-sad]
That is an unusual thing for a guideline to specify, and it is worth reading carefully. It is not “do not use light therapy”. It is “do not let somebody choose it instead of treatments that work, without knowing what they are choosing”.
Which gives a defensible position: a lightbox is inexpensive and low-risk, some people respond well, and it is a reasonable thing to try. It is not a reason to decline therapy or medication, and if it does nothing for you, that is a known outcome rather than a failure on your part.
Winter dip or something more?
Tick anything true of the last few winters. This is a reflection prompt rather than a test, and it produces no diagnosis.
0 of 8 ticked
The predictability is what makes this useful clinically: a mood change that arrives and departs on the calendar is exactly what the seasonal specifier describes. The last item is the common trap, since knowing it will lift in April is the reason people endure four months of it every year rather than treating it.
Feeling flatter in winter is very common and is not in itself a disorder. The line is cost: whether it changes what you are able to do, rather than only how you feel about the weather.
Nothing here matched. If low mood is present but not seasonal, our guide to dealing with depression covers the wider picture.
The free depression screener uses the PHQ-9. It measures the past two weeks, so for a seasonal pattern it is worth doing during the months that are difficult rather than in July.
What to do
Treat it as depression, because that is the classification. Psychological therapy and antidepressants both apply, and cognitive behavioural therapy adapted for seasonal depression has evidence including for reducing recurrence in later winters. [nice-ng222-sad]
Most of it works better started early. Getting ahead of winter low mood covers what to put in place in late summer, while starting anything new is still easy.
Start before it arrives. The single practical advantage of a predictable pattern is that you know the date. Arranging support in September is a different proposition from trying to arrange it in January while unwell.
Try a lightbox, with accurate expectations. Morning use, consistently, for a couple of weeks before judging. Knowing the evidence is uncertain means an absence of effect tells you something about the treatment rather than about you.
Get outside early. Free, and daylight outdoors is far brighter than indoor lighting. Treat it as a sensible habit rather than a proven intervention.
Do not wait it out on the grounds that it always lifts. Four months, annually, for a decade is a great deal of life, and the fact that it ends is not a reason to endure it.
Our guide to how to deal with depression covers treatment in more detail, and anhedonia covers the flatness that often persists after mood improves.
When to seek help
See a doctor if your mood changes predictably with the seasons and the low period affects your work, study, relationships or ability to look after yourself, particularly if it has happened for two years or more.
Mention the pattern explicitly, including the sleeping and eating changes, because the atypical presentation is easy to miss and it influences what gets offered.
Go urgently if you have thoughts of harming yourself.
How MyFreud can help
A seasonal pattern is invisible from inside a single winter and obvious across two, which is exactly the comparison memory cannot make. MyFreud gives you daily mood tracking that takes seconds, so when you tell a doctor it happens every year you have something to show rather than an impression.
Download MyFreud and start today: App Store or Google Play.