Writer gulps high tea if blissful (8)
I believe the answer is:
beatific
'blissful' is the definition.
(I've seen this before)
'writer gulps high tea if' is the wordplay.
'writer' becomes 'bic' (kind of pen).
'gulps' means one lot of letters goes inside another.
'high' is an anagram indicator (can mean drunk or on drugs and hence disordered).
'tea'+'if'='teaif'
'teaif' anagrammed gives 'eatif'.
'bic' going around 'eatif' is 'BEATIFIC'.
(Other definitions for beatific that I've seen before include "supremely happy" , "Showing great happiness, perhaps a smile" , "Joyful" , "Feeling or expressing blissful happiness" , "Angelic, saintly" .)