Clinical depression is not ordinary sadness. It is one of a number of serious illnesses called mood disorders that disrupt a person’s normal way of feeling, thinking and behaving. In major depressive disorder (MMD), a person suffers from feelings of hopelessness for long periods of time. Depression is marked by lack of energy and interest in regular activities and by changes in sleeping and eating patterns.
Persistent feelings of despair and debilitating physical symptoms—which can include muscle and joint pain, insomnia, and disruption of attention and memory—lead to suicide in 15% of people struggling with depression. Studies show that depression is also a contributing factor to life-threatening coronary disease.
The World Health Organization estimates that 350 million people suffer from depressive disorders. Depression can affect anyone at any age, from children to the elderly. It is nearly twice as common in women as men. But men tend not to seek treatment, so their depression may be under-reported. Patients suffering from other diseases, including cancer, stroke, diabetes and HIV, often experience depression.
Researchers do not yet know the specific causes of depression, but they do know that both short-term depression following extreme trauma, and life-long (chronic) depression involve the structure and chemistry of the brain. Research that focuses on chemical neurotransmitters—serotonin, norepinephrine and dopamine—has increased knowledge about depression and provided targets for drug therapies.