Vocalist, one shouting after swallowing too many drugs (8)
I believe the answer is:
yodeller
'vocalist' is the definition.
(yodeller is a kind of vocalist)
'after swallowing too many drugs' is the wordplay.
'after' becomes 'yeller' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'swallowing' means one lot of letters goes inside another.
'too many drugs' becomes 'OD' (abbreviation for overdose).
'yeller' enclosing 'od' is 'YODELLER'.
'one shouting' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for yodeller that I've seen before include "Singer using falsetto" , "Alpine singer" , "Vocalist" , "Mountain air for him" .)