Worried that millions of Americans are using prescription opiate painkillers to get high rather than to ease severe chronic pain, drug makers are working on ways to prevent abuse. Cooperating closely with government officials and pain specialists, the companies are educating doctors, rewriting warning labels and tracking pills as they move from pharmacy to patient. They are also reformulating pills with added ingredients. One combination blocks euphoria. Another produces a nasty burning sensation. "The problem of prescription painkiller abuse is much bigger than people realize," said Dr. Clifford Woolf, director of the neural plasticity group and professor of anesthesia research...