Someone who tries things is tense when cornered by a drug user (7)
I believe the answer is:
adopter
'someone who tries things' is the definition.
(as in an early adopter)
'tense when cornered by a drug user' is the wordplay.
'tense' becomes 't' (abbreviation used in many dictionaries).
'when cornered by' is an insertion indicator (corner can mean to trap or imprison).
'drug user' becomes 'doper' (someone who uses dope).
'a'+'doper'='adoper'
't' going inside 'adoper' is 'ADOPTER'.
'is' is the link.
(Other definitions for adopter that I've seen before include "One may take issue" , "who extends a family welcome?" , "A redtop (anag.)" , "person to accept another's child?" , "Person taking legal responsibility for a child not biologically theirs" .)