Correct end of nicotine patch (5)
I believe the answer is:
emend
'correct' is the definition.
(I've seen this before)
'end of nicotine patch' is the wordplay.
'end of' suggests the final letters.
'patch' becomes 'mend' (synonyms).
The final letter of 'nicotine' is 'e'.
'e'+'mend'='EMEND'
(Other definitions for emend that I've seen before include "would appear better" , "change" , "Make improvements or corrections" , "Make changes to (a text)" , "Improve by altering" .)