LOS ANGELES ? Troubled Hollywood starlet Lindsay Lohan has failed a drugs test and could face being thrown back behind bars for breaching her bail terms, reports said Friday.

The star, who was released from rehab last month after serving just three weeks of a six-month jail sentence over a drunk-driving case, failed the test for cocaine last week, said People magazine and the TMZ celebrity news agency.

There was no immediate direct word from Lohan or her agent, although US Magazine said she had responded to the reports by saying: "I'm fine," adding: "They're all nuts."

The Los Angeles Times quoted three sources as saying that authorities were investigating whether Lohan had failed a court-ordered drugs test.

Lohan was released last month, but a judge said she would remain under tabs for two months, and that any positive drugs test could result in her being jailed again for 30 days.

Lohan was sentenced on July 6 to 90 days in jail and another 90 days in rehab for violating her probation in a drunk-driving case. But due to jail overcrowding she served just 13 days, before being sent to the detox facility.

The actress was arrested three years ago for driving under the influence, and again two months after that for drunk driving and cocaine possession ? but served a mere 84 minutes in jail after the arrests.

The queen of Hollywood nights and a favorite target of the paparazzi, the former Disney child star was once considered one of the most promising actresses of her generation.

But Lohan's career has dipped many times since 2005 amid legal woes, stops in rehab and cinematic flops.

In 2008, the star of "The Parent Trap," "Mean Girls" and "Bobby" received two Razzie Awards, the satirical prizes presented to Hollywood's worst acting performances.