"Immune cytokine model of depression" suggests chronic inflammation as root cause

The idea that depression and other mental health conditions are caused by an imbalance of chemicals (particularly serotonin and norepinephrine) in the brain is so deeply ingrained in our collective psyche that it seems almost sacrilegious to question it. Of course Big Pharma has played a role in perpetuating this idea. Antidepressant drugs, which are based on the chemical imbalance theory, represent a $10 billion dollar market in the U.S. alone. According to the CDC, 11 percent of Americans over 12 years old take antidepressants, and they are the second-most prescribed medications (after cholesterol-lowering drugs). Doctors wrote a staggering 254 million prescriptions for antidepressants in 2010. (1) Yet as popular as this theory has become, it is riddled with problems. For example: Reducing levels of norepinephrine, serotonin and dopamine does not produce depression in humans, even though it appears to do so in animals.Although some depressed patients have low levels of serotonin and norepinephrine, the majority do not. Several studies indicate that only 25 percent of depressed patients have low levels of these neurotransmitters.Some depressed patients have abnormally high levels of serotonin and norepinephrine, and some patients with no history of depression have low levels of them. (2)What if depression isn't caused by a "chemical imbalance" after all? More specifically, what if depression itself is not a disease, but a symptom of an underlying problem? That is exactly what the most recent research on depression is telling us. A new theory called the "Immune Cytokine Model of Depression" holds that depression is not a disease itself, but instead a "multifaceted sign of chronic immune system activation." (3) To put it plainly: depression may be a symptom of chronic inflammation.