Score synthetic meth and use thus (5,5)
I believe the answer is:
sheet music
'score' is the definition.
(I've seen this before)
'synthetic meth and use thus' is the wordplay.
'synthetic' is an anagram indicator.
'and' is a charade indicator (letters next to each other).
'thus' becomes 'sic' (synonyms).
'meth' put after 'use' is 'usemeth'.
'usemeth' is an anagram of 'sheetmu'.
'sheetmu'+'sic'='SHEET MUSIC'
(Other definitions for sheet music that I've seen before include "Leaves with scores" , "Printed part for performer" , "printed notepaper?" , "score" .)