Though depression is a complex disease, the four major causes of depression are thought to be:
Genetics and brain chemistry. Research suggests that genes may be responsible for about half of all cases of depression. This means that if you have a relative who was diagnosed with depression, you're more likely to be diagnosed as well.
Substance abuse. Misusing certain substances can have a long-term effect on your brain chemistry. Many addictive substances trigger the release of your brain's "happy chemicals," like dopamine and serotonin, and your brain becomes dependent on these substances to feel normal. For many people who quit drugs, the psychological addiction is more difficult to overcome than the physical one.
Childhood experiences. Children who experience stress, neglect, or conflict, or receive constant criticism from loved ones seem to be more likely to develop depression.
Life events. When a person who is already susceptible to depression experiences a negative life event like a breakup, a divorce, or losing a job, they may develop depression.
Concerned you might be depressed? Take our free online depression quiz to determine whether you are experiencing symptoms of depression. Takes less than 3 minutes to get your results.