Superior Court Judge Rand Rubin ordered Kurt Cobain's widow to report to rehab by 5 p.m. local time, E! Online reported.
Prosecutors said Love suffered a drug overdose when she was recently rushed to a hospital from a Hollywood party. Love's reps, however, vigorously denied she was using drugs and said she had suffered a fainting spell.
She cried as she told the judge she was admitting to violating her probation by being under the influence of an unidentified controlled substance, E! said.
Love, who is on probation for assault and two unrelated drug cases, could also face jail time for the probation violation. She was ordered to re-appear in court Sept. 16 for sentencing and Rubin promised "further consequences at that time."
After Friday's hearing, Love's attorney told reporters his client was "serious," "sincere" and "pretty tenacious about getting her life in order."