Does order small portions of medications (5)
I believe the answer is:
doses
'portions of medications' is the definition.
'does order small' is the wordplay.
'order' is an anagram indicator.
'small' becomes 's' (abbreviation - e.g. clothes size).
'does' anagrammed gives 'dose'.
'dose'+'s'='DOSES'
(Other definitions for doses that I've seen before include "Gives medicine to" , "Measured amounts of medicine" , "Prescribed quantities of medicine" , "Quanitites of medicine" , "draughts" .)