Miles drunk inside as lacking purpose (7)
I believe the answer is:
aimless
'lacking purpose' is the definition.
(I've seen this in another clue)
'miles drunk inside as' is the wordplay.
'drunk' indicates an anagram.
'inside' indicates putting letters inside.
'miles' with letters rearranged gives 'imles'.
'imles' put within 'as' is 'AIMLESS'.
(Other definitions for aimless that I've seen before include "Without purpose or target" , "Drifting - Melissa (anag)" , "Without direction or ambition" , "Drifting with no purpose" , "Lacking a goal" .)