Causes

The direct cause of depression is unclear, but research shows certain factors can trigger a depressive disorder.

• Genetic factors. Some depression may be linked to genes. Some studies show a link with depression in biological families that was not found in families with adopted children.
• Chemical imbalances. People with depression may have imbalances in the natural substances that allow brain cells to communicate with one another.
• Life stresses. Any kind of life change, good or bad, can sometimes trigger depression. A job promotion can prompt a bout of depression as easily as a job loss. The birth of a child sometimes is followed by depression, as is the loss of a loved one.
• Medication. Depression may be caused by certain medications, such as pain relievers for arthritis, and certain medications for high blood pressure and heart problems.
• Physical problems. Physical changes in the body can be accompanied by mental changes as well. Medical illnesses such as stroke, a heart attack, cancer, Parkinson's disease and hormonal disorders can trigger depression. Sometimes depression is the first symptom of a serious condition like pancreatic cancer.
• Substance abuse. Experts believe 25 percent of people with substance abuse problems also have major depression. Drugs and alcohol provide a way for people to medicate themselves yet can lead to a downward spiral.
• Self-esteem issues. People with low self-esteem, who consistently view themselves and the world with pessimism or who are readily overwhelmed by stress are vulnerable to depression. Whether this represents a psychological predisposition or an early form of the illness is not clear.

A combination of genetic, psychological and environmental factors can contribute to the onset of a depressive disorder. Later episodes of depression can be brought on by mild stresses, or none at all.

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This article was reviewed and updated June 2007.