Patient information from BMJ

Seasonal affective disorder

Last published:Sep 29, 2022

If you have depression or bipolar disorder that gets worse in autumn and winter, or that only seems to happen at these times, it’s called seasonal affective disorder, or SAD for short.

If you think you may be affected by SAD, you can use our information to talk to your doctor about the best treatments for you.

What is seasonal affective disorder (SAD)?

SAD is often thought of as depression that only affects some people in autumn and winter. But this is only partly true. Most people with SAD have long-term depression that gets worse in these months.

SAD can also affect people with bipolar disorder. People with this condition have symptoms that can swing between depression and mania (feeling unusually excited and energetic).

When people with bipolar disorder are affected by SAD, their depression symptoms usually get worse in autumn and winter, and their mania symptoms improve in spring and summer. It can happen the other way around, but this is less common.

What causes SAD?

We’re not really sure. But it’s possible that lower levels of light in autumn and winter affect some of the body’s hormones. This, in turn, may affect some people’s mood.

One hormone in particular, called melatonin, is thought to be affected. This hormone helps to regulate our sleep patterns and our mood.

SAD also seems to be partly genetic. This means that it’s more common in people who have close relatives with the condition.

Other things we know about SAD include that:

• It usually begins between the ages of 20 and 30 years. It’s less likely to happen the older you get

• It’s not really clear how common it is in adults. Estimates vary between 1 and 10 in every 100 people

• It affects between 3 and 4 in 100 children and teenagers, especially girls during puberty, and

• It is between 3 and 5 times more common in women than in men.

What are the symptoms?

The symptoms of SAD are similar to those of depression, such as:

• Feeling low

• Lacking interest in things you usually enjoy

• Feeling hopeless and worthless, and

• Possibly thinking about harming yourself or about suicide.

But in the autumn and winter months people with SAD can also have different symptoms, including:

• Sleeping more than usual

• Wanting to eat more than usual, especially carbohydrates

• Gaining weight

• Moving slowly and sluggishly, and

• Feelings of heaviness in the limbs.

If you see your doctor about symptoms of SAD, they will ask you questions about your symptoms, and about your history of depression or bipolar disorder.

This helps your doctor to understand if and exactly how the condition affects you, and what treatments may help.

For example, your doctor will ask:

• How long you have been having symptoms

• What symptoms you have

• What time of year your symptoms begin, and

• What time of year your symptoms improve or go away.

Your doctor may also suggest blood tests to make sure nothing physical is causing your symptoms.

What treatments are available?

The aims of treatment for SAD are to:

• Help to control your symptoms, and

• Help you to get on with your life as normally as possible.

The two main treatments used to help people with SAD are:

• Light therapy. This involves using a special light box to mimic the effect of daylight on your body, and

• Antidepressant medicines.

Depending on your symptoms, your doctor may recommend that you start with one of these treatments, or that you have both together.

These two treatments seem to work about as well as each other, although light therapy seems to start to work more quickly. But you may find that you prefer one over the other for your own reasons. For example:

• Sme people may prefer light therapy if they are concerned about side effects of antidepressants

• Others may prefer medicines because they struggle to sit in front of a light box for long periods.

Light therapy

Light therapy involves sitting in front of a light box for between 30 minutes and two hours a day, depending on which box you use. Your doctor can advise you about which type you need.

When you are using the light box you need to stay awake and keep your eyes open. To pass the time you can read or listen to music.

With light therapy, symptoms usually start to improve within one to three weeks. It’s important to keep up the therapy, or symptoms can get worse again just as quickly.

Light therapy is not suitable for some people. For example, you shouldn’t use it if:

• You have a condition that affects your eyes, such as macular degeneration or problems with your retinas, or

• You are taking certain medicines. Your doctor should ask you about any medicines you are taking before prescribing light therapy or antidepressants.

Medicines

The main medicines used to treat SAD are antidepressants. There are many different ones, and you can talk to your doctor about the best option for you. 

Antidepressants can work well for SAD but they can take several weeks or more before they start to help with your symptoms.

All antidepressants can cause side effects in some people, including nausea, headaches, and insomnia. Your doctor should discuss these with you in detail. If side effects bother you a lot, talk to your doctor about switching to a different drug or a lower dose.

Some people with bipolar disorder also take medicines called mood stabilisers. These drugs help to control symptoms of mania. But these can cause side effects in some people, including shakiness, nausea, and dizziness.

Your doctor should discuss these with you carefully. If side effects bother you, talk to your doctor. You may be able to switch to a different drug or a lower dose.

If you are prescribed mood stabilisers, you may need to have blood tests from time to time.

Doctors sometimes prescribe mood stabilisers called valproates. These drugs can cause severe birth defects. If you are female and of childbearing age, your doctor should not prescribe these drugs unless:

• There is no alternative, and

• You and your doctor have made a pregnancy prevention plan.

Other treatments

Depression can make you feel sluggish and tired, so that you don’t feel like getting out and about or exercising. Sitting in front of a light box for a long time can also reduce the amount of time you spend being active.

So you may need to think about how you can stay active. Exercise is important for your physical health, and it can help to improve symptoms of depression.

Some doctors also recommend a 'talking treatment' called cognitive behavioural therapy (CBT) for some people.

Prevention

Doctors sometimes recommend treatments during the summer months, to help prevent the worst symptoms when the weather changes in autumn and winter. If you think that this is something that may help you, talk to your doctor.

What to expect in the future

Your doctor may suggest regular check-ups to see how your treatment is working. For example, they will probably stress the importance of keeping up your light therapy.

It’s not uncommon for people with depression and bipolar disorder to use alcohol or drugs to try to help with their symptoms. This can actually make symptoms worse by interacting with your medicines.

If you are concerned about problems with substance abuse, talk to your doctor about getting help.

In many people, SAD comes back year after year. So it’s important to keep up with your treatment.