Medicine or drug no-one returns (6)
I believe the answer is:
potion
'medicine' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'drug no-one returns' is the wordplay.
'drug' becomes 'pot' (slang term for cannabis).
'one' becomes 'i' (Roman numeral).
'returns' says the letters should be written in reverse.
'no'+'i'='noi'
'noi' backwards is 'ion'.
'pot'+'ion'='POTION'
'or' acts as a link.
Can you help me to learn more?
(Other definitions for potion that I've seen before include "Drink, maybe philtre" , "Medicinal draught" , "Magical liquid" , "Witches' brew" , "brew of Getafix?" .)