The most common and most likely answer to this crossword clue is the 13 letter word DECAFFEINATED
I've seen this crossword clue in The Sunday Telegraph
D
E
C
A
F
F
E
I
N
A
T
E
D
Buddy explains!
The straight part
We know that "As is a less stimulating cup" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case as is a less stimulating cup = decaffeinated.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 DECAFFEINATED mean?
DECAFFEINATED adjective- From which caffeine has been removed (e.g. decaffeinated coffee).