One consumed by work finally uses drugs (7)
I believe the answer is:
opiates
'drugs' is the definition.
(opiate is a kind of drug)
'one consumed by work finally' is the wordplay.
'one' becomes 'i' (Roman numeral).
'consumed by' means one lot of letters goes inside another (inserted letters get consumed).
'work' becomes 'op' (abbreviation for opus).
'finally' becomes 'ates' (I am not sure about this - if you are sure you should believe this answer much more).
'op'+'ates'='opates'
'i' inserted within 'opates' is 'OPIATES'.
'uses' acts as a link.
Can you help me to learn more?
(Other definitions for opiates that I've seen before include "Sedative drugs" , "Makes dull" , "Is a poet (anag.)" , "Poppy-derived drugs" , "Drugs that dull the feelings, sedatives" .)