She had appeared in front of a judge late last month over allegations that she failed two court-ordered drug tests and was told to spend a month in prison, but walked free after posting $300,000 bail.
The "Mean Girls" star subsequently checked herself into the Betty Ford clinic in Rancho Mirage, California and only left the centre in the early hours of Friday in preparation for her court hearing, reports imdb.com.
Lohan appeared before Judge Elden Fox at the Beverly Hills Courthouse in Los Angeles, Friday when she faced a three-month jail term. The judge has decided to keep the troubled star in a drug programme to help her kick her addictions once and for all.
"You are an addict. I hope you understand that," he told Lohan. The actress nodded in response and thanked Judge Fox for his lenient sentence.
Lohan has been ordered to stay in rehab until at least Jan 3 - meaning she will be spending the upcoming Christmas holidays in treatment. She will undergo random drug testing upon her release until her next court date Feb 25.