TLDR: This review suggests that the huge research effort based on the serotonin hypothesis has not produced convincing evidence of a biochemical basis to depres

TLDR: This review suggests that the huge research effort based on the serotonin hypothesis has not produced convincing evidence of a biochemical basis to depression. This is consistent with research on many other biological markers [21]. We suggest it is time to acknowledge that the serotonin theory of depression is not empirically substantiated.