Depression comes in 3 basic forms; physiological, emotional, and cognitive. "Depression" is the label given to the "urge to give up", to not act even when actions are available. The medical world defines depression as a state wherein a person retreats from "normal activity" for that person (much less definitive). The underlying cause of depression in all cases is the futilization of positive response.
Oppression often leads to depression whereas suppression offend leads to aggression (opposite of depression). The depressive state neither loves nor hates, but rather stops caring and insists in not caring. Depression is not merely the loss of hope, but the acceptance in the hope of retreating, "shutting down", "giving up". The urge to withdraw completely is what leads to suicidal depression. Suicide is the overt act to withdraw from all life entirely.
Biochemicals and drugs can help most with physiological depression wherein the body refuses to respond normally under normal stimuli. Exercise, increased bodily fluid flow, and a medically clean environment help most against physiological depression. Proper levels of vitamins and minerals can help if they happen to have become abnormal. This level of depression is classified as "disease" (dis-ease) and is generally caused by invasion of toxins or germs. Physiological depression is almost never caused genetically despite family history. More often the family merely experiences the same invasive affects, often from the same sources (environmental or social).
Drugs effect emotional depression through a complex reaction process where the feelings and emotors are medically tweaked until they mask the cause of the depression sufficiently to simulate normal behavior (what is assessed as such anyway). A strong change in life situation can greatly effect a depressive state, but the person will seldom choose to pursue such a change. Strong love or hate interests can jar the emotional state into seeing new hope in taking action. But if such changes in life are introduced and do not succeed, they instead further aid the depression. Emotional and cognitive depressions are never caused genetically regardless of family history.
Biochemicals and drugs have no effect on cognitive depression unless they have positive (or negative) effect on mental functions such as memory, attention, focus, concentration, analytical response, and so on. Nootropics aid in that regard. The cognitively perceived situation of the person is the cause of cognitive depression thus anything that appears to the person to yield hope in the person's situation works against cognitive depression (winning the lottery for example if money is an recognized issue).
Signs of each type of depression vary from each other. Some people have various degrees of each type. Each type affects each other type, but does not directly determine them. People sufficiently skilled to properly diagnose depression (or just about any psychological ailment) are difficult to find. This is largely due to the attempt to over simplify the mental state and assign labels through symptomology rather than addressing causes.
Social and economic depression are additional depression types caused by analogous affecters. These are most often brought about (along with personal depressions) as governments change hands or restructure. Futilizing the people's effort to maintain their own safety is a critical part of re-ording a society, thus the people sense and often recognized the hopelessness of their situation. Suicides rise sharply as social demonism is injected so as to make clay by crushing the former statue for sake of the new statue. In the West, the more recent change ("paradigm shift") came about as Christianity was replaced with Judeo-secularism for sake of world governing.
In all cases, depression is the result of the actions of others and is seldom remedied except by the same.