It makes people feel better to believe that their depression is the result of some chemical problem rather than something more mysterious and threatening having gone wrong.

The major textbooks agree that no chemical test exists that could distinguish a depressed person from a normal one.

What's more, an amazing variety of different chemicals are claimed to have an effect on depression. Even the leading drugs work by different supposed mechanisms. Stimulants (like amphetamines), tranquilizers, even botanicals such as St. John's Wort are claimed to work.