The most common and most likely answer to this crossword clue is the 5 letter word BOTOX
I've seen this crossword clue in The Guardian
B
O
T
O
X
Buddy explains!
The straight part
We know that "may result in a thick lip" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case may result in a thick lip = botox.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 BOTOX mean?
BOTOX verb- To inject Botox.
- Alternative letter-case form of Botox