Lohan, 21, was arrested early Tuesday in Santa Monica, California, and released on bail for investigation of misdemeanor driving under the influence and with a suspended license, and felony cocaine possession.
"I am innocent... did not do drugs they're not mine. I was almost hit by my assistant Tarin's mom I appreciate everyone giving me my privacy," Lohan wrote in an e-mail to "Access Hollywood" host Billy Bush, the show reported on its Web site Tuesday night.
Police found cocaine in one of the actress' pockets during a pre-booking search, Sgt. Shane Talbot said. Police initially said Lohan was also being booked for investigation of transporting a narcotic, but later said she was not.
Police received a 911 call from the mother of Lohan's former personal assistant, saying Lohan was chasing her in an SUV, Lt. Alex Padilla said. The assistant had quit hours before, he said.
Authorities found Lohan and the woman in a "heated debate" in a parking lot after midnight.
Lohan's also faces DUI allegations connected to a May hit-and-run crash in Beverly Hills, California. The actress completed more than six weeks in rehab on July 13, and checked into a recovery clinic in January.
She had worn an alcohol-monitoring ankle bracelet since rehab, and was tested daily to support her sobriety, her attorney Blair Berk said. She said Lohan had relapsed and was receiving medical care at an undisclosed location. Lohan's publicist had no comment.
Lohan joins a long list of young actors who battled problems with drugs, alcohol, or both. They include River Phoenix, Drew Barrymore, Corey Feldman, Anissa Jones, Danny Bonaduce and Macaulay Culkin.
Phoenix, who starred in "Stand By Me" as a teen, died outside a Hollywood nightclub in 1993 from a lethal combination of cocaine and heroin. He was 23. Feldman, his "Stand By Me" co-star, also battled addiction and was arrested for heroin possession when he was 19.
Jones, who played Buffy on TV's "Family Affair," was just 18 when she died of a drug overdose in 1976. Bonaduce found fame at 10 as a star of "The Partridge Family," only to struggle with addiction and homelessness as a teenager. Culkin, best known for his starring turn in the kid-friendly "Home Alone" films, was busted in his early 20s for possession of marijuana and Xanax.
Barrymore, 32, has fared best. After going to rehab for drugs and alcohol at 13, she is a sought-after actress and filmmaker with her own production company, Flower Films.
Dr. David Deitch, an addiction specialist for more than 40 years and director of Phoenix House, a national nonprofit provider of substance-abuse treatments, said the glitter and glamor of Hollywood could be partly to blame.
"That life is all about the excitement, drama and peak performance followed by a letdown that gets medicated with entertainment and medication," he said.
Deitch said the average age at which children start using drugs has dropped every decade since the 1960s, and that today's youngsters start experimenting with drugs about age 12.
"The earlier the age of onset of chronic drug-taking, the greater the prognosis is for long-term problems," he said.
Lohan was chastised last year for repeatedly arriving late to the set of "Georgia Rule," and her latest legal troubles may cost her movie roles. She was set to start shooting "Poor Things," a comedy featuring Shirley MacLaine, when she entered rehab in May. The film's producers, who previously had supported Lohan, would not say Tuesday whether she would be part of the production.
Lohan is still set to appear in the film "Dare to Love Me," which is to begin shooting this summer, said Michael Sands, a consultant for production company Bowline Entertainment.
"The producers have compassion and kindness for her," he said. "She hasn't been convicted of any crimes."
All Hollywood productions need insurance, and troublesome or troubled actors can often stand in the way of that requirement.
"I don't see how she's employable for the next 18 months," said longtime publicist Michael Levine, who does not represent Lohan. "Who's going to insure her?"
Lohan's latest film, "I Know Who Killed Me," is set to open Friday.