Actress Lindsay Lohan has failed her latest drug test, she admitted late Friday, and now faces the prospect of a return to jail.
Three weeks ago Lohan wrapped up her court-ordered rehab stint, supposedly clean and sober.
Per the terms of her probation in her DUI case as laid out last month by Judge Elden S. Fox, Lohan was "advised that any positive or missed test will result in 30-day jail sentence."
Late Friday, she revealed she had failed the test in a string of messages on the website Twitter.
"Regrettably, I did in fact fail my most recent drug test and if I am asked, I am prepared to appear before judge Fox next week as a result," she said.
"Substance abuse is a disease, which unfortunately doesn't go away over night. I am working hard to overcome it and am taking positive steps ... forward every day," she added. "I am testing every single day and doing what I must do to prevent any mishaps in the future."
"This was certainly a setback for me but I am taking responsibility for my actions and I'm prepared to face the consequences," Lohan wrote.
She concluded with a message to her "fans, loved ones and immediate family," saying she was thankful for their support.
They, Lohan said, "understand that i am trying hard, but also that I am a work in progress, just as anyone else. I am keeping my faith, and I am hopeful....Thank you all!!!"
The messages came after she had denied reports on the website TMZ of a failed drugs test, saying she was "fine" and, of TMZ, "they are all nuts."
It's not known what drugs were found in her system.
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A spokeswoman for the Los Angeles District Attorney's Office declined to comment. There was also no immediate word from Lohan's lawyer, Shawn Chapman Holley.
No hearing date has been announced.
Earlier this week LiLo was spotted in New York City, where she turned up at the Standard Hotel's recently reopened club Boom Boom Room. According to clubgoers, Lohan appeared to be on her best behavior, wasn't drinking and acted low-key.
She was back in L.A. Thursday, spotted lunching with her friend Lady Victoria Hervey.
E! Online, the Associated Press and US Magazine contributed to this report.