Poisonous substance manufactured in a European port (8)
I believe the answer is:
atropine
'poisonous substance' is the definition.
(I've seen this before)
'manufactured in a european port' is the wordplay.
'manufactured' indicates an anagram.
'european' becomes 'E' (abbreviation e.g. EU).
'in'+'a'+'e'+'port'='inaeport'
'inaeport' is an anagram of 'ATROPINE'.
(Other definitions for atropine that I've seen before include "Poison found in deadly nightshade used as a drug" , "Drug obtained from deadly nightshade" , "A pointer (anag) - belladonna" , "Poisonous substance" .)