The most common and most likely answer to this crossword clue is the 9 letter word ANTITOXIN
I've seen this crossword clue in The Daily Telegraph
A
N
T
I
T
O
X
I
N
More clues leading to the result ANTITOXIN
Buddy explains!

The straight part
We know that "remedy" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case remedy = antitoxin.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 ANTITOXIN mean?
ANTITOXIN noun- An antibody that is capable of neutralising specific toxins that are causative agents of disease.