I recently read two articles by a well known Christian author who is also closely connected to a Christian counseling foundation. The articles essentially argued that mental illness was a social construct created by secular doctors and psychiatrists, and therefore, is not biblical. So, when a person is depressed, he is really just experiencing sadness, and to try to treat it medically is to short circuit the power of God. When a person is anxious, she is really just experiencing worry, and to treat it medically is a secular answer to a spiritual problem. You get the idea.
The desire behind the article was good: the author was trying to demonstrate that Jesus is sufficient for every facet of life. However, I believe that treating mental illness as only (or even primarily) a spiritual problem is both profoundly unbiblical and incredibly hurtful to those who struggle with mental illness."