Hi MPRS,
8a - 6 letter word meaning "dopes" minus 2 letters for a "medical degree" - definition is "performances"
9d - 4 letter word for "hit" (informal according to Chambers) + 3 letter word for "head" minus last letter/"briefly" all reversed/"from below" - definition is an unusual meaning of "get rid of mouse"
5d - 6 letter word for "radical" (as in a chemical) + A(merican) - definition is "ways in"