Sometimes no such relationship can be found. There are environmental, biological, hereditary and developmental factors which may cause depression. Other medical illnesses and some medications may also cause depression. Most depression is probably the result of several factors interacting. Antidepressant drugs and other treatments are thought to work by correcting these imbalances.
Depression is one of the most common medical illnesses.
Depression is about twice as common in women as in men. There is a greater chance of becoming clinically depressed if you have a family history of depression. The likelihood of depression is much lower in less genetically similar relatives, but having any close relative with major depression increases the risk of becoming depressed. Still, the fact that even identical twins do not always share depression is evidence that there is more to depression than just genetics. There are a number of approaches to treating depression.