The most common and most likely answer to this crossword clue is the 8 letter word BOTULISM
I've seen this crossword clue in Financial Times
B
O
T
U
L
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M
More clues leading to the result BOTULISM
Buddy explains!
The straight part
We know that "which makes people sick" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case which makes people sick = botulism.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 BOTULISM mean?
BOTULISM noun- Poisoning caused by the toxin from Clostridium botulinum, a type of anaerobic bacteria that grows in improperly prepared food.