Were these patrons functioning members of society or outcasts? Were they seen as addicts or engaging in a recreational pastime?
From a more scientific standpoint, what is the chemical difference between this opium and the street heroin of today?
Thomas de Quincey's Confessions of an Opium Eater (1821) is essential reading in making headway in this question, although he is a street user. His work went on to be one of the primary sources for medical and anecdotal opium knowledge for many decades.
He paints opium usage as an underground and outsider activity, benefiting most those who were eschewed by the formal social status groups of the age. He noticed a profound effect on the experience of time, his thought processing, and of course the often pleasurable sedative feelings which one notices in all opiate drugs.