Depression is often, not always, a symptom of another disorder. This is especially true if your depression symptoms are acute or cyclical. Conditions like Bipol

Depression is often, not always, a symptom of another disorder. This is especially true if your depression symptoms are acute or cyclical. Conditions like Bipolar Disorder or ADHD are often mis-diagnosed as depression or anxiety. Beyond that, Depression could be caused by any of a myriad of internal or external variables. It is no wonder that it is notoriously difficult to study Depression when it might just be a symptom of a dozen distinct conditions. My anecdote is that I thought I experienced bouts of depression for no deeper reason right through my 20s. Turns out I have ADHD and my depression is just caused by my brain getting exhausted from masking/functioning.