Actor Zac Efron wore an Alcoholics Anonymous chip, suggesting he has been sober six months, to a recent Los Angeles basketball game, Zap2it.com said. The 26-year-old former "High School Musical" star has undergone treatment for drug and alcohol addiction at rehab facilities twice this year. He wore the AA chip around his neck when he attended a Los Angeles Lakers basketball game Dec. 20, the celebrity news website said Sunday.