Seasonal depression, or seasonal affective disorder (SAD), is a type of depression that returns around the same time each year, usually in fall and winter. A version of cognitive behavioural therapy built for SAD, called CBT-SAD, can ease symptoms, and in one large trial its benefits held up into a second winter. If low mood, oversleeping and pulling away from people shape your days each fall, depression counselling can help you plan ahead.
Seasonal depression is depression that follows the calendar. For most people it starts in late fall or early winter and lifts in spring, which is called winter-pattern SAD. A smaller group has the reverse, with symptoms in spring and summer. Episodes usually last about four to five months of the year (NIMH).
The signs are the same as other forms of depression, but they come and go at about the same time each year (CAMH). To meet the formal criteria, the seasonal episodes have to show up for at least two years in a row, and happen more often in that season than at other times of the year. A formal diagnosis comes from a physician, nurse practitioner, psychiatrist or psychologist. You don't need a diagnosis though to start talking to someone about how the season affects you.
The difference is how much it takes over your life. Lots of people feel a little flatter when the days get short. They still get through work, family and plans much as usual. Seasonal depression goes further. About 15 in 100 Canadians will have at least a mild form of it at some point in their lives, and about 2 to 3 in 100 will have a serious form (Canadian Psychological Association).
With winter-pattern SAD, a few signs tend to stand out alongside low mood:
If several of these show up every year and last for weeks, it's worth taking seriously. At Trillium, our depression therapists are Registered Social Workers (RSWs) or Registered Psychotherapists (RPs) who work with depression, including the kind that returns each fall and winter. You can meet them on our depression counselling page.
The main explanation is daylight. Less daylight seems to affect serotonin, a brain chemical that helps regulate mood, and people with winter-pattern SAD may make too much melatonin, the hormone that makes you sleepy (NIMH). Together, these changes can throw off your body clock, so sleep, energy and mood stop adjusting to the shorter days. Researchers are still working out the full picture.
In Ontario, the shift can feel sudden. The clocks fall back in early November (assuming this doesn't change, some provinces are looking to remove daylight savings - although days still get shorter either way), and darkness can arrive before many people leave work. Thoughts matter too. Many people with SAD carry heavy thoughts about winter, like dreading the dark months or feeling stuck indoors. It isn't clear whether these thoughts cause the low mood or come from it, but they're worth working on in therapy.
Seasonal depression is treatable, and the good news is that you don't have to just wait for spring. Talk therapy is one of the main treatments, and it's used for both the winter and summer patterns (NIMH). It can help on its own or alongside other care, depending on what you need (CAMH).
Your doctor or nurse practitioner can talk with you about medical options, such as antidepressants or vitamin D, and whether they make sense for you (sometimes a blood test is reccomended to test for vitamin D deficciency). Those are decisions to make with them, and many people combine that care with therapy. Everyday habits matter too. Moving more and spending more time outdoors may help ease symptoms, which is why the planning tips further down focus on daylight, routine and things to look forward to.
Dreading another dark season? In a free 20-minute matching consult, you can tell our intake team what fall and winter are like for you, and they'll suggest a Trillium therapist who fits, with no pressure to book.
Book a free matching consultTherapy can help you change the patterns that winter tends to set off. A version of cognitive behavioural therapy (CBT) built for SAD, called CBT-SAD, does two main things. You learn to notice and question the heavy thoughts that come with the season. You also plan and schedule activities you enjoy, indoors and out, to push back against the urge to hibernate. Therapists call that second part behavioural activation.
The research on how long the benefits last is encouraging. One trial followed 177 adults with winter depression for two winters after treatment. By the second winter, symptoms had come back for about one in four of the people who'd had CBT-SAD (American Journal of Psychiatry). This is a single study, but it suggests that skills learned in therapy can keep helping long after sessions end.
Our depression therapists draw on CBT and related approaches, and they adapt the work to how winter shows up in your life. You can meet in person in Waterloo or through online counselling anywhere in Ontario. Online sessions can help on days when getting out the door feels like too much.
A little planning in the fall can make winter feel more manageable. A few things many people find helpful:
If the holidays tend to leave you drained, our article on the post-holiday slump covers that stretch in more detail. And if you're not sure whether what you feel is enough to reach out for, these signs it might be time to book therapy may help you decide.
If the darker months keep pulling you down, you don't have to wait them out alone. A free 20-minute chat with our intake team is a low-pressure way to talk about what you're looking for and get matched with a therapist who fits, with no commitment.
Book a Free ConsultationLearn more about depression counselling at Trillium
No. The winter blues are a mild dip in mood or energy that doesn't stop you from living your life. Seasonal depression is a form of depression: low mood most of the day, nearly every day, for at least two weeks, along with changes in sleep, appetite, energy or interest, returning at about the same time each year (NIMH).
Can you get seasonal depression in the summer?Yes, though it's less common. Summer-pattern SAD tends to look different from the winter kind, with trouble sleeping, poor appetite, restlessness and anxiety rather than oversleeping and cravings (NIMH). Talk therapy can help with either pattern.
Does seasonal depression come back every year?It often does, because seasonal depression follows a recurring pattern. Not everyone with SAD has symptoms every year, though (NIMH). Skills from therapy, like planning activities you enjoy and working with heavy thoughts about winter, can help you get ahead of it each fall.
Does vitamin D help seasonal depression?It might help some people, but the research is mixed. Many people with winter-pattern SAD have low vitamin D, yet studies testing vitamin D as a treatment have had mixed results (NIMH). Ask your doctor before starting a supplement, and don't rely on it as your only support.
When should I get help for seasonal depression?Before the darkest months, if you can. If you've noticed the same slide in past years, early fall is a good time to start. You can build a plan while you still have some energy. If you're already struggling, now is a good time too. You don't need to wait for things to get worse.
If you or someone you know needs support right now, help is available:
About the reviewer — Devon Jorge, MSW, RSW, Registered Social Worker, Psychotherapist — Devon is Clinical Director at Trillium Counselling and a Registered Social Worker authorized to perform the controlled act of psychotherapy. She reviews Trillium’s educational articles to keep them accurate and responsible. Last reviewed October 2026.
About this article — This article is intended for general education about mental health and the therapy process. It is not a substitute for professional diagnosis, treatment, or individualized mental health advice. If you have concerns about your mental health, please speak with a qualified health professional or contact local crisis services in an emergency.