The most common and most likely answer to this crossword clue is the 3 plus 8 letter word THE MUNCHIES
I've seen this crossword clue in The Guardian
T
H
E
M
U
N
C
H
I
E
S
Buddy explains!
The straight part
We know that "desire to eat after smoking a joint" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case desire to eat after smoking a joint = the munchies.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.