The initial availability of the drugs was from a prescription. If it weren't for the ready availability of the drugs, far fewer people would be addicted.
People are addicted to pain killers usually because they are dealing with pain, and they are either medicating or self-medicating to manage it.
If mere availability of something addictive was the problem, then we'd have a nation of nothing but alcoholics and cigarette smokers considering you can buy either in an unlimited quantity at any corner store.
If mere availability of something addictive was the problem, then we'd have a nation of nothing but alcoholics and cigarette smokers considering you can buy either in an unlimited quantity at any corner store.