Depression is not a diagnosis. The diagnosis is "iatrogenic depression", "substance abuse related depression", "pervasive depressive disorser", "bipolar disorde

Depression is not a diagnosis. The diagnosis is "iatrogenic depression", "substance abuse related depression", "pervasive depressive disorser", "bipolar disorder related depression", "developmental disorder related depression", "adjustment disorder" and only very finally there is the "idiopathic major depressive disorder" and a few gradations thereof, which is the trashcan. And I've probably skipped a few. (E.g. genetic folate metabolism disorder, thyroid related) Treatments are different in each. Lead, mercury and some other heavy metal exposure is one of iatrogenic. They are not commonly tested as they are rare causes and tests are not specific. (As opposed for thyroid panel and folate check which are highly specific.)