Yes, Harlem did play a role in leading Sonny to start using heroin. In line 76, the narrator says that he is bringing Sonny "back into the very danger he had almost died trying to escape." This shows us that Sonny had turned to heroin as he couldn't handle living in the devastating city he grew up in. Harlem is full of poverty, and there are prostitutes frequenting the streets. There is crime occurring but, for young boys like Sonny and the narrator, there is even more danger below the surface. This danger is how difficult it is to break free of the poverty and crime when growing up in the situation. This inability to rise above is what led Sonny to begin using heroin as a way to cope.