I've read an interview with Nick Cave, who lived in West Berlin in the 1980s and was a drug addict. He said that the "stuff" was very cheap and good - by that he probably meant very pure. And he said that the word on the street was that the drugs must have been supplied by communists to undermine western capitalists. Has this been researched?
Also, from various media I got the impression that West Berlin had a high number of drug addicts. Was that really much above European average?
EDIT: google search yields a few articles from the 1970s and 1980s that seem to support the view that heroin was in fact very available in West Berlin at that time.