Queen's picked up laxative for driver (5)
I believe the answer is:
senna
'laxative for driver' is the definition.
'senna' can be an answer for 'driver' (racing driver Ayrton Senna, 1960-1994). I am unsure of the 'laxative for' bit.
'queen's picked up' is the wordplay.
'queen's' becomes 'anne's' (Queen Anne, 18th-century queen).
'picked up' shows that the letters should be reversed in order.
'annes' reversed gives 'SENNA'.
(Other definitions for senna that I've seen before include "Cassia tree, laxative" , "Leaf used as laxative" , "Anne's upset by a laxative" , "purgative's needed" , "should make you want to go quickly" .)