Writing in The New Yorker, Michel Pollan points out:

The human brain is perhaps the most complex system there is, and the emergence of a conscious self is its highest achievement. By adulthood, the mind has become very good at observing and testing reality and developing confident predictions about it that optimize our investments of energy (mental and otherwise) and therefore our survival. Much of what we think of as perceptions of the world are really educated guesses based on past experience (“That fractal pattern of little green bits in my visual field must be a tree”), and this kind of conventional thinking serves us well.

But only up to a point. Dr. Robin Carhart-Harris notes that a steep price is paid for the achievement of order and ego in the adult mind. “We give up our emotional lability," he said, "our ability to be open to surprises, our ability to think flexibly, and our ability to value nature.”  The sovereign ego can become a despot. This is perhaps most evident in depression, when the self turns on itself and uncontrollable introspection gradually shades out reality.  In The Entropic Brain, a paper published last year in Frontiers in Human Neuroscience, Dr. Carhart-Harris cites research indicating that this debilitating state, sometimes called “heavy self-consciousness,” may be the result of a “hyperactive” default-mode network.  

Dr. Carhart-Harris believes that people suffering from depression and other mental disorders characterized by excessively rigid patterns of thinking, such as addiction and obsessive-compulsive disorder, could benefit from psychedelics, which “disrupt stereotyped patterns of thought and behavior.” In his view, all these disorders are, in a sense, ailments of the ego. He also thinks that this disruption could promote more creative thinking. It may be that some brains could benefit from a little less order.

As previously noted here. other research has shown that meditation has much the same effect on the brain's default-mode network as psychedelic drugs.  So at the risk of offending the pharmacology industry, the treatment for disorders such as depression addiction, and OCD may not be the use of drugs, but instead the practice of meditation.