The entertainment site quoted the Park County Coroner as saying that Kidder died from an intentional drug and alcohol overdose.
The daughter of late Superman star Margot Kidder has urged people experiencing mental health difficulties to seek help after a coroner's office in the United States released its ruling on her mother's death.
Kidder struggled with mental illness much of her life, and it was made worse by a 1990 vehicle accident that left her in debt and led to her using a wheelchair for nearly two years. "It's important to be open and honest so there's not a cloud of shame in dealing with this".
Now, nearly three months after Kidder's body was found by a friend in her Livingston, Montana home, a coroner there has ruled her death a suicide.More news: Iran clients tweaking U.S. sanctions as $90 oil looms
Kidder and Reeve starred in four Superman movies between 1978 and 1987.
McGuane noted that Montana has one of the highest suicide rates in the nation and she urged people with mental illness to seek help.
While no further details will be released of her suicide, McGuane added that "it's a unique sort of grief and pain and that she would like to reach out to every family who is suffering through a loss by suicide".
Most recently, Margot appeared in The Neighbourhood, which came out earlier this year.
A serious vehicle accident in 1990 left Kidder temporarily unable to work, putting her in debt.