Performing rota, yearn for medication (8)
I believe the answer is:
atropine
'medication' is the definition.
(I know that atropine is a type of antispasmodic)
'performing rota yearn' is the wordplay.
'performing' is an anagram indicator (the letters move around or 'perform').
'yearn' becomes 'pine' (synonyms).
'rota' with letters rearranged gives 'atro'.
'atro'+'pine'='ATROPINE'
'for' acts as a link.
(Other definitions for atropine that I've seen before include "Poisonous substance" , "Poison found in deadly nightshade used as a drug" , "Drug obtained from deadly nightshade" , "A pointer (anag) - belladonna" .)