Actor Hayden Panettiere died from an accidental drug overdose that included fentanyl, a South Carolina coroner confirmed Tuesday.

Emergency responders were called to a residence where Panettiere had been staying in Greenville, South Carolina on the afternoon of August 16. Despite "advanced cardiac life support measures," she was pronounced dead there, the Greenville County Coroner's Office said.

An autopsy by the coroner's office found that Panettiere's death was accidental and ruled that the cause was the "toxic effects of" the drugs fentanyl, 4-ANPP, alprazolam, methocarbamol and quetiapine.

There were no signs of trauma, the coroner's office said.

Panettiere's on-again, off-again boyfriend Brian Hickerson and his brother Zach were at the scene of her death, according to a police report obtained by CBS News. The Hickersons made the 911 call that brought first responders to the apartment.

The police report said Brian Hickerson showed officers "the bag of medication" that Panettiere was "currently on," but the list of substances was redacted. Zach Hickerson later told TMZ that Brian gave Panettiere Narcan, a medication that can reverse opioid overdoses, after they found her unconscious at the residence.

Authorities, including the Drug Enforcement Administration, were investigating the circumstances of Panettiere's death. Police previously said that a preliminary investigation "has not indicated any signs of foul play or suspicious circumstances."

Before her death at age 36, Panettiere was open about her prior struggles with drugs and alcohol abuse. She said she became addicted to alcohol and opioids as a teenager. She also discussed addiction in her recent memoir, "This Is Me: A Reckoning," as well as describing her experiences with physical abuse, postpartum depression and recovery.

Panettiere told CBS News' Gayle King in May that she hoped sharing her story would help others.

"I really wanted to share with the world that they don't have to be afraid. That they can live their truth. They can be imperfect," she said in the interview. Asked how she was doing, she replied, "Still working on myself all the time. I had a great therapist and I'm — I'm better, healthier than I've been in a long time."

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