Los Angeles County Sheriff's spokesman Steve Whitmore said Lohan left jail at 1:35 am local time before being transferred immediately to a substance abuse treatment center to begin a 90-day stint.
The treatment facility was not identified, but Whitmore said Lohan had left the prison in a minivan with multiple individuals, the report said.
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The Radar Online website reported Lohan was being treated at the Ronald Reagan UCLA Medical Center.
Lohan has been locked up at the Century Regional Detention Facility in Los Angeles since July 20 but she was kept away from other inmates for security reasons.
Lohan, who starred in the 1998 film "The Parent Trap" and 2003's "Freaky Friday," was arrested in May 2007 after crashing her Mercedes in Beverly Hills.
After a stay in rehab, the star of "Mean Girls" and other hit films was caught two months later for drunk driving and cocaine possession. At the time, she spent a mere 84 minutes in jail.
The actress has completed an alcohol education program, but was found in violation of probation because she did not attend classes regularly.
Despite a tough period adjusting to jail life, Lohan remained cooperative and became more subdued as days passed, according to law enforcement sources quoted by the Los Angeles Times.
