McCready, 28, who became a star at 18 with her debut No. 1 single "Guys Do It All The Time," was taken into custody Thursday at her home and charged with prescription drug fraud, E! Online said.
McCready, who has no criminal record, is out of jail on $10,000 bail.
McCready has bounced between record labels for the past decade, never repeating her early success. Her last project, a self-titled album on Capitol Nashville, sold so few copies that Capitol dropped McCready from its roster.
In recent years, she has become better known for her romances, including a brief engagement in 1997 to actor Dean Cain, who starred as Superman on TV's "Lois and Clark," and a Saudi Arabian prince.
OxyContin, a highly addictive opiate sometimes called hillbilly heroin, has been a vice for several celebrities, including Matthew Perry, Winona Ryder, Courtney Love and Jack and Kelly Osbourne, E! said.