Nick Reiner was diagnosed with schizophrenia before Sunday's murder of his parents, Rob and Michele Reiner, TMZ reported.
The medication Nick was taking made him "erratic and dangerous," two sources told TMZ.
Nick, who was seeing a psychiatrist for his mental illness, exhibited alarming behavior in the month leading up to the killings, according to the entertainment news organization.
The sources told the outlet that doctors had recently changed Nick's medication, making him even more erratic.
Doctors were working to adjust his medicine to stabilize him but were unsuccessful, TMZ reported.
He had been receiving care at a Los Angeles-based rehab center that specialized in mental illness and substance abuse at a cost of $70,000 a month, the report stated.
"Nick was out of his head," a source told the news organization about the change to his medication.
Nick's substance abuse also made the schizophrenia worse, sources said.
The son of the legendary actor and director Rob Reiner made his first court appearance Wednesday on two counts of first-degree murder in the killing of his parents.
The 32-year-old Nick Reiner did not enter a plea as he appeared from behind the glass wall of a custody area.
He was in shackles and wearing a jail suicide prevention smock.
Nick Reiner's arraignment was postponed until Jan. 7 at his lawyer's request.
He spoke only to say "Yes, your honor" to agree to the date.
Along with the two counts of first-degree murder, prosecutors added special circumstances of multiple murders and a special allegation that the defendant used a dangerous weapon, a knife.
The additions could mean a greater sentence.
TMZ believes Nick will plead not guilty by reason of insanity.
Los Angeles County District Attorney Nathan Hochman said his office has not decided whether to seek the death penalty in the case.
Rob Reiner was the Emmy-winning star of the sitcom "All in the Family" who went on to direct films including "When Harry Met Sally ..." and "The Princess Bride."
He was an outspoken liberal activist for decades.
Michele Singer Reiner was a photographer, movie producer, and advocate for LGBTQ+ rights.
They were married for 36 years.
The Associated Press contributed to this report.
Sam Barron ✉
Sam Barron has almost two decades of experience covering a wide range of topics including politics, crime and business.
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