Labels for the first long-acting opioid addiction treatment device are rolling off printing machines Friday. Trainings begin Saturday for doctors who want to learn to insert four matchstick-size rods under the skin. They contain the drug buprenorphine, which staves off opioid cravings. The implant, called Probuphine, was approved by the Food and Drug Administration on Thursday, and is expected to be available to patients by the end of June.