Depression is the most widespread psychological malady there is. Just in the United States, it's believed that twenty percent of the adult population has depression. Putting that percentage into a number comes to roughly sixty million people in the US, most of whom don't get a depression diagnosis or any form of treatment. With such a high affliction rate, considering the causes of depression is an obviously worthwhile endeavor.

There are essentially two reasons for depression: biological factors and environmental interactive factors. A combination of biological and environmental factors is obviously another possibility. When discussing biological causes of depression, essentially what's being referenced is a chemical imbalance in the brain. Various chemicals function in complex ways within the brain. There's a correlation between low levels of particular chemicals within the brain and emotional and psychological dysfunctions, depression included.

One of the chemicals believed to have a primary function in the regulation of mood is serotonin. Low serotonin levels have been associated not only with depression but with obsessive-compulsive disorder, anxiety, sleep difficulties, and anger and aggression abnormalities. The discovery of serotonin in the role of mood was key in the development of the selective serotonin reuptake inhibitor class of drugs, also known as SSRI's. Of the SSRI's, and there are now a number available, Prozac was the first on the market and is still the most well known. Prozac in fact is one of the most widely prescribed pharmaceuticals in history, a testament to the prevalence of depression and emotional malaise.

The belief that depression is entirely an environmental interactive issue is the other side of the coin in the thinking on what causes depression. That is to say, depression isn't caused by any biological imbalance at all but instead occurs because of how a person responds to their environment. As one example, an individual may consider the break up of a relationship as a significant loss and fall into a depression as a result. From an environmental interactive position the thinking would be that this particular depression isn't due to some brain dysfunction but is instead caused by the significance this person attaches to a life event: a relationship break up in this particular case. Using this sort of explanation, all forms of depression can be explained by a person's perspective as opposed to any biological factors.

Is depression then caused by biological factors or by how one considers the environment they inhabit? The answer is likely a combination of both. The effectiveness of drugs like Prozac demonstrate that there is a biological element to depression, but there's certainly also issues of perspective at work as well.