PITTSBURGH POST-GAZETTE - Christina Mair has a question: What causes addiction? Studying alcohol and marijuana use in California, Ms. Mair focused on the social determinants that might lead to dependency. While genetics play a role, she learned, it’s often environmental factors that lead a user to take his first hit (or sip). Everything from a community’s demographics to the presence of liquor stores on its streets can impact levels of addiction. When Ms. Mair moved to Pittsburgh in the midst of an epidemic three years ago, she wondered whether opioid dependency worked the same way.