Drug's power overcoming poor sleeping policeman (5,4)
I believe the answer is:
speed bump
'sleeping policeman' is the definition.
(I've seen this before)
'drug's power overcoming poor' is the wordplay.
'drug' becomes 'speed' (speed is a kind of drug).
'power' becomes 'p' (symbol in physics).
'overcoming' indicates putting letters inside.
'poor' becomes 'bum' (both can mean poor quality).
'speed'+'p'='speedp'
'speedp' enclosing 'bum' is 'SPEED BUMP'.
(Other definitions for speed bump that I've seen before include "Traffic-calming device" , "Sleeping policeman" , "traffic checker" , "Traffic-calming measure (B, not H)" , "Sleepng policeman" .)