“Heroes” and “Nashville” star Hayden Panettiere’s death has been ruled an accident caused by the toxic effects of multiple drugs, including fentanyl, officials said Tuesday.

The Greenville County Coroner’s Office attributed her cause of death to the toxic effects of fentanyl, 4-ANPP, Alprazolam, Methocarbamol and Quetiapine.

There were no signs of trauma that would have contributed to the death, the release added.

Panettiere, 36, died Aug. 16 at a South Carolina apartment complex where she had been staying. Authorities found her unresponsive after a report of a cardiac arrest.

The Greenville Police Department said there were no signs of foul play during the initial response and investigation. The investigation into her death remains active, the department said Tuesday.

The Drug Enforcement Administration was also investigating Panettiere’s death.

Bill Bodner, the former special agent in charge of the DEA’s Los Angeles Field Division, noted that the quantity of drugs found in Panettiere’s system remains unclear. But three of the drugs listed in her autopsy became common among drug abusers in the 1990s and remain widely used.

The cocktail’s street name, he said, is “the Holy Trinity.”

Bodner identified those drugs as an opiate, which in Panettiere’s case was fentanyl; a muscle relaxer, or Methocarbamol; and an anti-anxiety medication, or Alprazolam.

Quetiapine is an antipsychotic drug typically used to treat conditions such as schizophrenia, bipolar disorder and major depressive disorder. 4-ANPP, or 4-Anilinopiperidine, is a precursor chemical used in the illicit manufacture of fentanyl, Bodner said.

He described the precursor as a likely sign that the fentanyl found in her system was illegal. The drug cocktail, he added, is “incredibly dangerous.”

“When used in combination, there’s a synergism,” he said.

Panettiere’s on-again, off-again boyfriend, Brian Hickerson, was at the apartment complex at the time of her death and showed authorities what a police report described as a “bag of medication” he said she was taking.

An attorney for Hickerson did not immediately respond Tuesday to a request for comment on Panettiere’s death. Panettiere’s mother, Lesley Vogel, also did not immediately respond to a request for comment Tuesday.

Bodner, who probed the overdose deaths of Michael Jackson, Matthew Perry and other celebrities, has said investigators were likely attempting to reconstruct Panettiere’s final days.

“They will use forensics to exploit her telephone, try to re-create the last two or three days of her life from looking at text messages, looking at phone calls, looking at interaction with people on social media,” the 32-year veteran of the DEA’s field office in Los Angeles said.

“Once there’s a timeline of what she was doing before her death, it becomes easier to kind of find where that drug distribution took place that killed her,” Bodner added.

Panettiere’s relationship with Hickerson — an aspiring actor from South Carolina — appeared to have ended in 2020 amid allegations of domestic violence, but her mother told NBC News that they were still seeing each other when she died.

Panettiere detailed those allegations, along with her struggles with addiction and postpartum depression, in her recently released memoir, “This Is Me: A Reckoning.”

Hickerson pleaded no contest to a charge of injuring a spouse or girlfriend in 2019 in Los Angeles, and he was sentenced to four years of probation, court records show. Panettiere sought a restraining order against Hickerson in 2020, though the outcome is unclear.

In a statement in August, a lawyer for Hickerson reiterated that police found no signs of foul play in Panettiere’s death. The attorney, Sloan Ellis, added that the actor’s death remained under investigation.

“Out of respect for Hayden’s loved ones and the ongoing investigation, there will be no further comment at this time,” Ellis said at the time.

Panettiere began appearing in television commercials as a child. She landed a breakout role on the NBC sci-fi series “Heroes” and later earned two Golden Globe nominations for portraying an ambitious and volatile country musician in “Nashville.”

In her memoir, Panettiere wrote that her life began to spiral after she had a daughter with Ukrainian heavyweight boxing champion Wladimir Klitschko in 2014. She began drinking heavily to cope with postpartum depression and Klitschko’s distance, she wrote.

Panettiere checked into rehab and gave Klitschko custody of their child in 2018.

If you or someone you know is struggling with a drug or substance abuse problem, call these numbers for help: The Substance Abuse and Mental Health Services Administration’s national helpline is 1-800-662-HELP (1-800-662-4357); the National Drug Helpline is 1-844-289-0879; and the American Addiction Centers’ hotline is (866) 464-3073.