What Causes Depression?

Medically Reviewed by Jabeen Begum, MD on April 22, 2024
7 min read

Depression is a complex disease. No one knows exactly what causes it, but it can happen for a variety of reasons. Some people have depression during a serious medical illness. Others may have depression because of big life changes such as a move or the death of a loved one. Some people also have a family history of depression and may feel overwhelmed with sadness and loneliness for no known reason.

Lots of things can increase the chance of depression, including:

Abuse. Physical, sexual, or emotional abuse can make you more vulnerable to depression later in life.

Age. If you're elderly, you're at a higher risk of depression. And factors such as living alone and lacking social support can add to the risk.

Certain medications. Some drugs, such as isotretinoin (used to treat acne), the antiviral drug interferon-alpha, and corticosteroids, can increase your risk of depression.

Conflict. If you have frequent personal conflicts or disputes with family members or friends, it may make you biologically vulnerable to depression.

Death or a loss. Sadness or grief after the death or loss of a loved one, though natural, can increase your risk of depression.

Gender. Women are about twice as likely as men to become depressed. No one's sure why. The hormonal changes that women go through at different times of their lives may play a role.

Genes. A family history of depression may increase the risk. It's thought that depression is a complex trait, meaning there are probably many different genes, with each exerting small effects, rather than a single gene leading to disease risk. The genetics of depression, like most psychiatric disorders, is not as simple as that of purely genetic diseases, such as Huntington's chorea or cystic fibrosis.

Major events. Even good events such as starting a new job, graduating, or getting married can lead to depression. So can moving, losing a job or income, getting divorced, or retiring. However, the syndrome of clinical depression is never just a "normal" response to stressful life events.

Other personal problems. Problems such as social isolation due to other mental illnesses or being cast out of your family or social group can add to your risk for clinical depression.

Serious illnesses. Sometimes, depression happens along with a major illness or may be triggered by another medical condition.

Substance misuse. Nearly 30% of people with substance misuse problems also have major or clinical depression. Even if drugs or alcohol temporarily make you feel better, they ultimately will worsen your depression.

Researchers have noted that the brains of people who have clinical depression differ from those of people who do not. For instance, the hippocampus, a small part of the brain that is vital to the storage of memories, appears to be smaller in some people with a history of depression than in those who've never been depressed. A smaller hippocampus has fewer serotonin receptors. Serotonin is one of many brain chemicals known as neurotransmitters. These chemicals allow communication across circuits that connect the brain regions involved in processing emotions.

Scientists don't know why the hippocampus may be smaller in some people with depression. But some research shows that the stress hormone cortisol is produced in excess in depressed people, and cortisol has a toxic or "shrinking" effect on he hippocampus. Some experts think depressed people may simply be born with a smaller hippocampus and are thus inclined to have depression. There are many other brain regions and pathways between specific regions that are thought to be involved with depression. Probably, there is no single brain structure or pathway that fully accounts for clinical depression.

One thing is certain — depression is a complex illness with many contributing factors. The latest scans and studies of the brain structure and function suggest that antidepressants can exert "neurotrophic effects." That means they can help sustain nerve cells, prevent them from dying, and allow them to form stronger connections to withstand biological stresses. As scientists gain a better understanding of the causes of depression, health professionals will be able to make better "tailored" diagnoses and, in turn, prescribe more effective treatment plans.

We know that depression can sometimes run in families. This suggests that there's at least a partial genetic link to depression. Children, siblings, and parents of people with severe depression are more likely than the general population to have depression. Multiple genes interacting with one another in special ways probably lead to the various types of depression that run in families. Yet, despite the evidence of a family link to depression, it's unlikely that there is a single "depression" gene. Rather, many such genes, each with a small effect, contribute to depression when they interact with the environment.

Heredity appears to play an even bigger role in more severe forms of depression. Whether you inherit the tendency toward depression from your mother's side or your father's also seems to make a difference. One study found that women were more likely to inherit a tendency toward depression than men, and some genetic risk factors vary based on sex.

In certain people, drugs may lead to depression. Drugs that have been linked to depression include:

If you take three or more medications that are linked to depression, your risk of depression is higher.

In some people, a chronic illness can cause depression. A chronic illness is one that lasts a very long time and usually cannot be cured completely. However, they often can be controlled through diet, exercise, lifestyle habits, and certain medications.

Examples of chronic illnesses linked to depression include:

Researchers believe that treating depression may sometimes also help improve the coexisting medical illness.

When pain lingers for weeks to months, it's called "chronic." Not only does chronic pain hurt, but it also disturbs your sleep, your ability to exercise and be active, your relationships, and your productivity at work. Chronic pain may also leave you feeling sad, isolated, and depressed.

Researchers aren't sure how the link between chronic pain and depression works. They're investigating brain structures, neurotransmitters, and pathways for signaling. They aim to look for treatments that might improve depression linked to chronic pain.

There is help for chronic pain and depression. A multifaceted program of medicine, psychotherapy, support groups, and more can help you manage your pain, ease your depression, and get your life back on track.

Grief is a common, normal response to loss. Losses that may lead to grief include the death or loss of a loved one, loss of a job, death or loss of a beloved pet. Any other major life changes, such as divorce, becoming an "empty nester," or retirement, can also cause grief.

Grief and major depression can overlap, but there are some differences. For instance:

Waves of feeling. If you're grieving, you'll probably have periods of intense sadness, but you'll also have positive memories. When you have major depression, your mood is almost always negative.

Self-esteem. Grief doesn't usually affect your feelings of self-worth. If you have major depression, you're likely to feel worthless at times and experience self-loathing.

Researchers know that a loss can lead to a bout of major depression. It might be more likely if you have an underlying mental health issue or you've gone through other recent losses. Major depression can cause your grief to last longer and be more intense.

Depression is a complicated condition that has many causes. Researchers have found links to brain structures, family history, medications, other illnesses, and chronic pain. A history of trauma can raise your risk for depression. You're also more likely to have depression if you're older or a woman. Grief is a natural response to loss and can trigger major depression, which in turn can make grief last longer.

What leads to depression in a person?

Researchers suggest that the causes of depression include genetic, biological, psychological, and environmental factors. If you're dealing with depression, it probably stems from a combination of factors rather than just one thing.

Can depression be caused by someone else?

Depression usually doesn't have one single cause. It's usually the result of several factors. But the kind of support you receive from people around you can influence whether negative events in your life lead to depression.