The most common and most likely answer to this crossword clue is the 9 letter word OVERDOSED
I've seen this crossword clue in Independent
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More clues leading to the result OVERDOSED
Buddy explains!

The straight part
We know that "having had too much Coke?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case having had too much coke? = overdosed.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 OVERDOSED mean?
OVERDOSED verb- To dose excessively, to take an overdose.
- To indulge in something excessively.
- To dose to excess; to give an overdose, or too many doses, to.