Drug could have bearing on the case (8)
I believe the answer is:
sedative
'drug' is the definition.
(I know that sedative is a type of medicament)
'bearing on the case' is the wordplay.
'bearing' becomes 'SE' (south east, a compass bearing).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'the case' becomes 'dative' (the dative case in grammar).
'se'+'dative'='SEDATIVE'
'could have' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for sedative that I've seen before include "Drug to make one sleep" , "Sleeping drug" , "Tranquillising drug" , "having soothing effect" , "Dates I've changed for a tranquiliser" .)