Cannabis can make you cough quietly (4)
I believe the answer is:
hemp
'cannabis' is the definition.
(I've seen this before)
'you cough quietly' is the wordplay.
'you cough' becomes 'hem' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'quietly' becomes 'p' (p for piano and quiet).
'hem'+'p'='HEMP'
'can make' acts as a link.
Can you help me to learn more?
(Other definitions for hemp that I've seen before include "Source of drug" , "Plant for rope or pot" , "Grass" , "tea" , "Rope-making fibre" .)