The most common and most likely answer to this crossword clue is the 9 plus 4 letter word NICOTINIC ACID
N
I
C
O
T
I
N
I
C
A
C
I
D
Buddy explains!
The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.