It's obvious I've been upset by depression (7)
I believe the answer is:
evident
'it's obvious' is the definition.
(similar in meaning)
'i've been upset by depression' is the wordplay.
'been upset' says the letters should be written in reverse (I've seen 'being upset' mean this).
'by' is a charade indicator (letters next to each other).
'depression' becomes 'dent' (synonyms).
'ive' back-to-front is 'evi'.
'evi'+'dent'='EVIDENT'
(Other definitions for evident that I've seen before include "Plain to see" , "Plain, obvious, clear" , "Quite obvious, manifest" , "clearly visible" , "Comprehensible - manifest" .)