Public health experts say the abuse of prescription medication is the fasting-growing drug problem in the United States. A new Obama administration initiative aims to reduce addiction levels by 15 percent over the next five years. Among others elements, it would require doctors to receive special training for prescribing painkillers. Many in law enforcement laud the proposals. But people who need powerful drugs to manage chronic pain are concerned. They fear tougher rules for physicians will make it harder for them to get relief. An update on what’s being called a public health epidemic.