The most common and most likely answer to this crossword clue is the 9 letter word CRACKHEAD
I've seen this crossword clue in Financial Times
C
R
A
C
K
H
E
A
D
More clues leading to the result CRACKHEAD
Buddy explains!

The straight part
We know that "an addict" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case an addict = crackhead.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.
What does CRACKHEAD mean?
CRACKHEAD noun- A person who is addicted to or regularly uses crack cocaine.
- Someone whose thinking makes no sense; a fool or an idiot.