More drugs that heartless lags will inject (4)
I believe the answer is:
else
'more' is the definition.
(synonyms)
'drugs that heartless lags will inject' is the wordplay.
'drugs' becomes 'E' (somebody 'on E' could also be 'on drugs').
'that heartless' suggests removing the centre.
'will inject' becomes 'e' (I am not sure about this - if you are sure you should believe this answer much more).
'lags' with its middle removed is 'ls'.
'e'+'ls'+'e'='ELSE'
Can you help me to learn more?
(Other definitions for else that I've seen before include "In addition, besides" , "Besides; instead" , "In addition; different" , "Other than (what is under consideration)" , "Besides, otherwise" .)