Suffer ruin, recklessly taking cocaine (5)
I believe the answer is:
incur
'suffer' is the definition.
(to incur is to suffer or experience)
'ruin recklessly taking cocaine' is the wordplay.
'recklessly' indicates anagramming the letters.
'taking' is an insertion indicator.
'cocaine' becomes 'C' (drugs abbreviation).
'ruin' is an anagram of 'inur'.
'inur' enclosing 'c' is 'INCUR'.
(Other definitions for incur that I've seen before include "contract" , "Meet" , "Become responsible for" , "Bring something on oneself, often unpleasant" , "Invite, bring about" .)