The most common and most likely answer to this crossword clue is the 4 letter word TOKE
I've seen this crossword clue in The Times
T
O
K
E
Buddy explains!

The straight part
We know that "a drag" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a drag = toke.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 TOKE mean?
TOKE noun- (casinos) A gratuity.
- To give a gratuity to.
- A puff of marijuana.
- To smoke marijuana.
- To inhale a puff of marijuana
- A piece of bread.