Does order small amounts of medicine (5)
I believe the answer is:
doses
'amounts of medicine' is the definition.
(a dose is a prescribed amount of medicine)
'does order small' is the wordplay.
'order' is an anagram indicator.
'small' becomes 's' (abbreviation - e.g. clothes size).
'does' with letters rearranged gives 'dose'.
'dose'+'s'='DOSES'
(Other definitions for doses that I've seen before include "Medicates" , "Medicine measures" , "Gives medicine to" , "Quanitites of medicine" , "Specific quantities" .)