Perhaps Washington Post journalist took drugs (4)
I believe the answer is:
used
'took drugs' is the definition.
(to use can mean to take drugs)
'perhaps washington post journalist' is the wordplay.
'perhaps washington post' becomes 'us' (I am not sure about this - if you are sure you should believe this answer much more).
'journalist' becomes 'ed' (short for editor).
'us'+'ed'='USED'
(Other definitions for used that I've seen before include "Utilised" , "Took advantage of" , "Worn" , "Second-hand, not new" , "Sued, having been employed" .)