How Is Biology Related to Depression? continued...

Scientists do not know why the hippocampus may be smaller in some people with depression. Some researchers have found that the stress hormone cortisol is produced in excess in depressed people. These investigators believe that cortisol has a toxic or "shrinking" effect on the development of hippocampus. Some experts theorize that depressed people are simply born with a smaller hippocampus and are therefore inclined to suffer from depression. There are many other brain regions, and pathways between specific regions, thought to be involved with depression, and likely, no single brain structure or pathway fully accounts for clinical depression.

One thing is certain -- depression is a complex illness with many contributing factors. The latest scans and studies of brain chemistry suggest that antidepressants can help sustain nerve cells and allow them to form stronger connections that withstand biological stresses (called "neurotrophic effects"). As scientists gain a better understanding of the causes of depression, health professionals will be able to make better "tailored" diagnoses and, in turn, prescribe more effective treatment plans.

How Is Genetics Linked to the Risk of Depression?

We know that depression can sometimes run in families. This suggests that there's at least a partial genetic link to depression. Children, siblings, and parents of people with severe depression are somewhat more likely to suffer from depression than are members of the general population. Multiple genes interacting with one another in special ways probably contribute to the various types of depression that run in families. Yet despite the evidence of a family link to depression, it is unlikely that there is a single "depression" gene, but rather many genes that each contribute small effects toward depression when they interact with the environment.

Can Certain Drugs Cause Depression

In certain people, drugs may lead to depression. For example, medications such as barbiturates, benzodiazepines, and the acne drug Accutane have sometimes been associated with depression, especially in older people. Likewise, medications such as corticosteroids, opioids (codeine, morphine), and anticholinergics taken to relieve stomach cramping can sometimes cause mania, which is a highly elated and energized state that can also be associated with bipolar disorder.