Fisher, 60, went into cardiac arrest while on a flight to London to Los Angeles on December 23.
Her mother, movie star Debbie Reynolds, died of a stroke the following day.
The cause for Fisher's apparent heart attack on the plane was never really explained - until now, as a Los Angeles County Coroner has revealed the official cause of the Carrie Fisher's death. Additionally, he told the site, "I am not shocked that part of her health was affected by drugs", noting prescriptions she took to treat her mental health. According to the Associated Press, the report stated Fisher had taken multiple drugs prior to her death.
Additional autopsy and toxicology details were not available.
Officials could not conclusively determine a cause of death, the AP said.
Numerous drugs were prescribed by doctors to try and treat her mental health conditions, he said.
A successful author, Fisher had written and spoken openly about her struggle with drugs abuse in her youth and mental health issues. "They contained me", she said.
Fisher had always been open about her struggle with bipolar disorder and substance abuse issues, starting at only age 13 when she began smoking marijuana. She was treated with electroshock therapy and medication.
"If you want to know what killed her, it's all of it", he said.
Todd Fisher said it was hard to blame doctors who treated his sister because they were trying to help her.
He doesn't blame doctors however, saying they were "doing their best to cure a mental disorder".
Aside from Star Wars, Fisher was known from roles in When Harry Met Sally, The Blues Brothers, and most recently, the Amazon comedy series Catastrophe.