Efficient medical treatment out of bounds (4)
I believe the answer is:
able
'efficient' is the definition.
(I've seen this before)
'medical treatment out of bounds' is the wordplay.
'medical treatment' becomes 'tablet' (type of medication).
'out of bounds' says to take the centre (the bounds or edges of the word are removed).
The central letters of 'tablet' are 'ABLE'.
(Other definitions for able that I've seen before include "Having the necessary capacity (to do something)" , "Clever skilful" , "Competent as seaman may be" , "See 21" , "Showing skill" .)