In a statement, the Park County, Montana, coroner’s office confirmed to the wire service that the actress “died as a result of a self-inflicted drug and alcohol overdose."
Kidder was found dead at her home in Livingston, Montana, on May 13 at the age of 69. At the time, a spokesperson said that the actress passed away peacefully in her sleep.
Speaking to the Associated Press on Wednesday, Kidder’s daughter, Maggie McGuane, said that she knew her mother had taken her own life when she was brought to Kidder’s home. “It’s a big relief that the truth is out there,” McGuane said, adding: “It’s important to be open and honest so there’s not a cloud of shame in dealing with this.”
The actress had publicly struggled with mental-health issues. She had been diagnosed with bipolar disorder and, in 1996, she suffered a public manic episode and nervous breakdown.
Although her body of work spanned six decades and encompassed more than a hundred projects, the actress will always be best known, and beloved, for her career-defining turn as Lois Lane in four Superman films starring opposite Christopher Reeve, from 1978’s Superman: The Movie to 1987’s Superman IV: The Quest for Peace.