The most common and most likely answer to this crossword clue is the 5 letter word OPIUM
I've seen this crossword clue in The Times
O
P
I
U
M
More clues leading to the result OPIUM
- Powerful drug: one taken with expression of doubt after operation
- Work on island with hesitation, producing narcotic drug
- Number with hatred for decimalisation?
- Narcotic: retired army doctor secures more in Milan
- Narcotic I dump at the centre, after work
- Constant unrest primarily in order, justification for war once?
- Order includes more Italian analgesic
- Drug is used mainly at first after surgery
- A number of poppies?
- Poppy product‘s opening triad is lifted from heavy metal
Buddy explains!

The straight part
We know that "Powerful drug" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case powerful drug = opium.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 OPIUM mean?
OPIUM noun- A yellow-brown, addictive narcotic drug obtained from the dried juice of unripe pods of the opium poppy, Papaver somniferum, and containing alkaloids such as morphine, codeine, and papaverine.
- Anything that numbs or stupefies.