For the latest news on Lindsay Lohan, watch HLN's "Showbiz Tonight" live at 11am ET on Monday.
Los Angeles, California (CNN) -- Lindsay Lohan acknowledged through Twitter postings Friday night that she failed a recent drug test, but the actress said she's "working hard to overcome" her drug addiction.
Lohan's supervised probation for a 2007 drunken driving conviction requires frequent drug tests. The judge warned her last month any failure could send her back to jail.
"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," Lohan tweeted Friday evening.
She spent 23 days in a court-ordered drug rehab program last month, which followed a 13-day jail stint imposed when a Los Angeles judge ruled that Lohan violated her probation.
Judge Elden Fox, who took over Lohan's case when she was released, imposed a new set of rules for her to follow until November. It included weekly counseling sessions for alcohol and drug rehab, random drug tests and behavioral therapy.
Lohan's lawyer did not respond to CNN requests for comment Friday. A spokesman for the Los Angeles County district attorney also declined to comment.
No new court date has been announced for Lohan to face Judge Fox concerning the failed drug test.
"Substance abuse is a disease, which unfortunately doesn't go away overnight," Lohan tweeted. "I am working hard to overcome it and am taking positive steps."
Lohan tweeted that she was "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," she tweeted.
Lohan made fun of her substance abuse troubles in a backstage skit broadcast during last Sunday's MTV Video Music Awards.
She appeared with show host Chelsea Handler, who was wearing an alcohol-detection bracelet like the one Lohan recently wore.
"Wake up, Handler, pull it together," Lohan said as she slammed Handler against a wall. "You're a menace. Do you think anyone will work with a drunk? Take it from me, they don't."