Whoa, that's an outsized proportion - entire Germany has 77k people in methadone substitution: http://www.bfarm.de/SharedDocs/Downloads/DE/Bundesopiumstell...
Also, the numbers are 500 methadone substituters (of total ~1k opiate users) in Paderborn (http://www.nw.de/lokal/kreis_paderborn/paderborn/paderborn/1...). What would interest me is the background why ~1% of the population are opiate abusers, though.