No, it’s not “all in your head.” Depression and all of its relatives are manifestations of glitches in the immune system and inflammatory pathways—not a neurochemical deficiency disorder.
Psychiatry: A Very Special Specialty
Psychiatry, unlike other fields of medicine, is based on a highly subjective diagnostic system. Essentially you sit in the office with a physician, and you are labeled based on the doctor’s opinion of the symptoms you describe. There are no tests. You can’t pee in a cup or give a drop of blood to be analyzed for a substance that definitely indicates “you have depression” much in the way a blood test can tell you that you have diabetes or are anemic.