Greek character lies with no-one's drug couriers (5)
I believe the answer is:
mules
'drug couriers' is the definition.
'mules' can be an answer for 'couriers' (mule can informally mean a courier of drugs). I am unsure of the 'drug' bit.
'greek character lies with no-one's' is the wordplay.
'greek character' becomes 'mu' (letter of the Greek alphabet).
'with no' suggests deleting specific letters.
'one' becomes 'i' (Roman numeral).
'lies' with 'i' taken away is 'les'.
'mu'+'les'='MULES'
Can you help me to learn more?
(Other definitions for mules that I've seen before include "Offspring of male donkeys and female horses" , "Backless slippers" , "Obstinate people" , "Stubborn horse-donkey animaly" , "Hybrid offsprings of a male donkey and a female horse" .)