The most common and most likely answer to this crossword clue is the 5 plus 3 letter word GRAND CRU
I've seen this crossword clue in Independent
G
R
A
N
D
C
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U
More clues leading to the result GRAND CRU
- £1000 getting a lot of rubbish wine
- Magnificent rowing team picked up famous wine
- Magnificent men on board said to make wine
- Fine wine, relative filth finally coming first
- Wine
- Fine wine as well as cold game served by a king
- Foreign bread caught among a lot of food and special wine
- Fine wine and piano gets workers in voice
- Type of wine from republic’s borders put in food mostly
- Magnificent party, we hear — top quality wine
Buddy explains!
The straight part
We know that "and drug can start to react oddly (5,3)" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case and drug can start to react oddly (5,3) = grand cru.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.