Animal on opioids loses ego — gets high (6)
I believe the answer is:
isopod
'animal' is the definition.
(isopod is a kind of animal)
'opioids loses ego gets high' is the wordplay.
'loses' suggests deleting specific letters.
'ego' becomes 'i' ('I' in Latin).
'gets high' is an anagram indicator (high can mean drunk).
'opioids' with 'i' taken out is 'opoids'.
'opoids' anagrammed gives 'ISOPOD'.
'on' acts as a link.
(Other definitions for isopod that I've seen before include "This crusty creature" , "Crustacean such as a woodlouse" , "Member of an order of crustaceans" , "Crustacean with seven pairs of legs for crawling" , "Slater, for instance" .)