What causes depression

There is no single cause of depression. Experts agree that genes, brain biology, life experiences and the way a person thinks all play a part.¹ Most of the time, several of these come together at once.⁶

Knowing the causes can ease guilt. Depression is not a weakness or a choice. It also helps you see what you can change, such as sleep, drinking, loneliness or a medicine that may be making things worse.

A mix of causes, not one

Think of depression risk like a scale. Some weights push toward depression, such as family history, a hard childhood, illness or a recent loss. Other weights push back, such as close relationships, regular movement and good sleep.

Scientists say that a person's surroundings and genes work together to set their overall risk.² Two people can go through the same loss. One may grieve and slowly recover. The other may slide into depression. Neither person did anything wrong.

Genes and family history

Depression runs in families. If a parent, brother or sister has had it, your chance of getting it is about two to three times higher than average.²

Twin studies help show how much of this is passed down in genes. A large review of these studies estimated that genes explain a bit more than one third (about 37%) of the differences in risk between people.³ That means most of the risk comes from other things, such as life events and health.

There is no single "depression gene." Many genes each add a very small amount of risk. Some of these genes affect brain chemical messengers. Others affect how brain cells grow and form connections.²

Families also share homes, habits and hardships, not just genes. So a family pattern is partly about the life you grew up in.⁶

Brain and body biology

Depression is linked to real changes in the brain and body. Researchers have found that depression is tied to:⁵

• Stress hormones that stay out of balance for a long time
• Inflammation (the body's defense response, which can cause harm when it stays switched on)
• Changes in blood flow and heart rate control

Some illnesses change the brain directly. Parkinson's disease and stroke are two examples. These brain changes can lead to depression on their own, apart from the stress of being ill.⁵

Sleep matters too. Poor sleep and depression feed each other. Sleep problems are listed as one of the factors that can bring on depression.⁶ Learn more in Sleep, mood and anxiety.

The "chemical imbalance" idea, explained carefully

For many years, ads and even some doctors said depression is caused by a "chemical imbalance," mainly low serotonin (a brain chemical messenger). Many people still believe this.

In 2022, a team of researchers pulled together the main reviews on serotonin and depression. They found no consistent evidence that low serotonin causes depression.⁴ For example:

• Levels of serotonin or its breakdown products did not clearly differ in people with depression.⁴
• Lowering serotonin in healthy volunteers mostly did not cause low mood.⁴
• Large, high-quality gene studies found no link between depression and a gene for the serotonin transporter (the protein that recycles serotonin).⁴

The review had limits. Many of the studies it looked at were small or of low quality. Many did not fully account for past use of antidepressants.⁴

Here is what this does and does not mean:

Stress and life events

Hard events are some of the most common triggers. These include:^2,6

• Death of a husband, wife, family member or friend
• Divorce or relationship trouble
• Losing a job, money worries or debt
• Being cut off from other people

Later in life, other changes can raise the risk. Examples include moving out of your home, children moving far away, losing the ability to drive, or needing help with daily care.⁷ Caring for a family member with dementia can also be heavy and lonely. See our caregivers section.

Grief after a death is normal and is not the same as depression. But sometimes grief turns into depression. See Grief for how to tell the difference.

Childhood hardship

What happens in childhood can matter for a lifetime. Abuse, neglect, and growing up with violence or a parent's mental illness are called adverse childhood experiences, or ACEs.⁹ Long-lasting stress in childhood can affect how the brain and stress systems develop. This can make depression more likely later in life.⁹ Childhood abuse and neglect are well-known risk factors.²

ACEs are common. In a CDC survey, about 3 in 4 high school students reported at least one.⁹ Having had ACEs does not doom anyone. Support, safe relationships and treatment can help at any age.

Illness and pain

Living with a long-term illness raises the risk of depression.⁵ This includes:^5,7

• Heart disease and stroke
• Diabetes
• Cancer
• Chronic pain
• Thyroid disease, especially an underactive thyroid
• Parkinson's disease, multiple sclerosis and dementia

The link goes both ways. People with depression are more likely to develop heart disease, diabetes, stroke and other conditions. When both are present, each one tends to be more severe.⁵ Read more in Depression with heart disease, stroke, diabetes and pain.

Some conditions, such as thyroid problems, can cause symptoms that look like depression. That is why a doctor checks for them.¹ See Getting checked for depression.

Medicines

Some medicines can cause side effects that add to depression.¹ Steroid medicines (such as those for asthma flares or arthritis) are one known example.⁶ Some sleep aids can make depression worse in older adults.⁷

If your mood changed after starting a new medicine, tell your doctor. Bring a full list of everything you take, including over-the-counter pills and supplements. Do not stop a prescribed medicine on your own. Your doctor may be able to switch it or change the plan.

Alcohol and drugs

Alcohol and drug use can bring on depression.⁶ Drinking too much can also make existing depression worse.⁷

Depression and alcohol problems often go together. About 27% to 40% of people with major depression (roughly 1 in 3) have an alcohol use disorder at some point in life.⁸ Some people drink to numb their feelings. But heavy drinking can lead to longer low periods, thinking problems and a higher risk of suicide.⁸

The good news: when people stop drinking, their mood often gets better.⁸ If you are unsure whether your low mood is caused by alcohol, it can help to tell your doctor how your mood was before you started drinking heavily, or during times you did not drink.⁸

Loneliness

Social isolation and loneliness raise the risk of depression and anxiety. Depression can also make people pull away, so the two feed each other.¹⁰ About 1 in 3 U.S. adults say they feel lonely.¹⁰ See Loneliness.

What protects against depression

You cannot change your genes or your past. But some things seem to lower the risk.

Small steps count. A daily walk with a friend, a phone call, or joining a group can add up. For more ideas, see Self-help for depression and practices like loving-kindness and tai chi.

In later life

Depression is not a normal part of aging. But older adults often face more of the risk factors at once: illness, pain, many medicines, loss of loved ones, and loss of independence.^1,7 Brain changes from stroke or dementia can also play a role.^5,7

In older adults, depression may look less like sadness and more like a lack of feeling, low energy or memory trouble.¹ Learn more in Depression in later life and on our older adults page.

When to get help

Whatever the cause, depression is treatable. You do not need to find the cause before you get help.

• If low mood, loss of interest or hopelessness last two weeks or more, talk with your doctor. You can start with our check-in.
• If your mood changed after a new medicine, or you are drinking more to cope, tell your doctor.
• If you or someone you know is thinking about suicide, call or text 988 (the Suicide & Crisis Lifeline) any time, day or night.⁵
• If someone is in immediate danger, call 911.

See Signs and symptoms of depression, Treatment for depression, and Get help.

Education only. This page is general information written from the sources listed. It is not medical, legal or financial advice and does not replace a doctor, therapist or lawyer who knows your situation. How we write and check pages.