Game's up for contraceptive (4)
I believe the answer is:
loop
'contraceptive' is the definition.
(type of intrauterine device)
'game's up' is the wordplay.
'game' becomes 'pool' (pool is a kind of game).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'pool' in reverse letter order is 'LOOP'.
'for' acts as a link.
(Other definitions for loop that I've seen before include "Oval or U-shaped coil or bend" , "not informed one's out of it" , "flying stunt" , "Closed circuit eg as hearing aid" , "Complete circuit; encircle" .)