A patient watched pictures appear one by one. First, a bicycle. Next, a treat: a cupcake. Then a picture of the drug heroin. Researchers followed her brain’s reactions to the sight of the drug that she has tried to stop taking. U.S. government scientists are starting to study the brains of people caught in the opioid epidemic in the United States. They want to see if medicines proven to treat substance abuse, like methadone, do more than ease the person’s desire for the drug. Do these medicines also heal a brain damaged by drug dependency? Which medicine works best for which patient? Studies have found that three medicines can effectively treat what specialists are calling opioid use disorder. They are methadone, buprenorphine and extended-release naltrexone.