The most common and most likely answer to this crossword clue is the 4 letter word LUSH
I've seen this crossword clue in Financial Times
L
U
S
H
Buddy explains!

The straight part
We know that "Drinker/flourishing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case drinker/flourishing = lush.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 LUSH mean?
LUSH adjective- Juicy, succulent.
- Mellow; soft; (of ground or soil) easily turned; fertile.
- (of vegetation) Dense, teeming with life; luxuriant.
- (of food) Savoury, delicious.
- (miscellaneous) Thriving; rife; sumptuous.
- Beautiful, sexy.
- Amazing, cool, fantastic, wicked.
- Lax; slack; limp; flexible.
- Drunkard, sot, alcoholic.
- Intoxicating liquor.
- (Pidgin) A person who enjoys talking about themselves
- To drink (liquor) to excess.