The most common and most likely answer to this crossword clue is the 8 letter word ASPIRINS
I've seen this crossword clue in The Guardian
A
S
P
I
R
I
N
S
More clues leading to the result ASPIRINS
Buddy explains!

The straight part
We know that "They manage sir’s pain /They manage sir’s pain" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they manage sir’s pain /they manage sir’s pain = aspirins.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 ASPIRINS mean?
ASPIRINS noun- An analgesic drug, acetylsalicylic acid
- A tablet containing this substance