Relative in French resort taking drug (5)
I believe the answer is:
'relative' is the definition.
(type of relative)
'french resort taking drug' is the wordplay.
'french resort' becomes 'Nice' (French coastal resort).
'taking' means one lot of letters goes inside another.
'drug' becomes 'e' (E is another name for ecstasy).
'nice' enclosing 'e' is 'NIECE'.
'in' acts as a link.
(Other definitions for niece that I've seen before include "Family relative" , "A sibling's child" , "Daughter of a sibling" , "Female family member" , "Preparation for curdling milk" .)