The coroner's office confirmed that Panettiere, best known for her roles in the TV series Heroes and Nashville, died last month at the age of 36 after being found unresponsive at a residence in South Carolina. The autopsy also identified the presence of methocarbamol, a prescription muscle relaxant, and quetiapine, an antipsychotic medication.
According to the coroner's office, emergency responders initiated advanced cardiac life support measures, but resuscitation efforts were unsuccessful. The US Drug Enforcement Agency (DEA) was reportedly joining the local police department's investigation into Panettiere's death.
A police report from the day she died noted that Panettiere's ex-boyfriend, Brian Hickerson, who has admitted to abusing her, and his brother Zack were with her when emergency services arrived. Panettiere had spoken openly about her struggles with substance abuse and postpartum depression. Just months before her death, she published a memoir discussing these issues in detail.
Fentanyl, a synthetic opioid implicated in the drug, has been linked to hundreds of thousands of deaths in the US over the past five years.