The most common and most likely answer to this crossword clue is the 13 letter word ANTIBACTERIAL
I've seen this crossword clue in The Daily Telegraph
A
N
T
I
B
A
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T
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More clues leading to the result ANTIBACTERIAL
Buddy explains!

The straight part
We know that "Like a drug" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case like a drug = antibacterial.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 ANTIBACTERIAL mean?
ANTIBACTERIAL noun- A drug having the effect of killing or inhibiting bacteria.
- (pharmaceutical effect) Killing or inhibiting bacteria.
- Opposing the theory that diseases are caused by bacteria.