Extra problem with drugs, when losing heart (8)
I believe the answer is:
addition
'extra' is the definition.
(I've seen this before)
'problem with drugs when losing heart' is the wordplay.
'problem with drugs' becomes 'addiction'.
'when losing heart' says to hollow out the word (remove centre letters).
'addiction' with its centre removed is 'ADDITION'.
(Other definitions for addition that I've seen before include "Increment" , "plus" , "Calculation of the sum of two or more" , "Process of summation" , "Mathematical process" .)