Addiction is chemically induced. The regions of the brain associated with pleasure are responsible for releasing dopamine. Excessive use of heroin, alcohol or any other kind of drug will illicit this response from your brain.
I'm no scientist, but I do know that alcoholism and addiction implusles can indeed be hereditary. I'm Irish. I have that tendency to overindulge after taking several sips of beer (Good stuff, like Corrona or Boulevard).