Work with one university doctor starts to explore new systems in drug centres (5,4)

'drug centres' is the definition.
(places where opium is taken)

'work with one university doctor starts to explore new systems' is the wordplay.
I cannot quite understand how this works, but
'work' could be 'op' (abbreviation for opus) and 'op' is found in the answer.
'one' could be 'i' (Roman numeral) and 'i' is located in the answer.
'university' could be 'u' (abbreviation for university) and 'u' is found in the answer.
'doctor' could be 'md' (synonyms) and 'md' is found in the answer.
'new' could be 'n' (common abbreviation eg NT for New Testament) and 'n' is found within the answer.
The remaining letters 'es' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

'in' is the link.