EXCLUSIVE: How Hayden Panettiere's Zebra Fall Sparked Decades of Pain and Drug Abuse

Hayden Panettiere suffered more than two decades of physical pain after being thrown from a zebra as a teenage actress – an injury she later said contributed to the opioid use that became part of her long struggle with addiction.

As Radaronline.com reported, Panettiere, 36, was found unresponsive at a residence in Greenville, South Carolina, on Sunday, August 16, after traveling there with on-again, off-again boyfriend Brian Hickerson.

Authorities have found no evidence of foul play and have not announced a cause of death, although dispatch audio referenced a suspected overdose and cardiac arrest.

Narcan was reportedly discovered inside the apartment, but it remains unknown whether it was administered to Panettiere.

A source familiar with Panettiere's struggles told Radar in an exclusive interview: "That accident became much more than something that happened to Hayden on a movie set as a teenager. She wrote about still experiencing the consequences more than 20 years later, and when the old injury became painful again, opioids became part of that story."

Another Hollywood insider added: "Hayden's addiction had many complicated elements and nobody should reduce it to one event. But the physical pain was real; she connected increased opioid use to her neck injury flaring up, and it was something she was still dealing with decades after the accident. It was what really prompted her downward spiral into drugs and depression."

Panettiere was 14 when she was thrown from a zebra while making Racing Stripes, released in 2005.

In her memoir, This Is Me: A Reckoning, published three months before her death, Panettiere said the accident damaged two vertebrae in her neck and caused severe whiplash and a concussion.

She wrote: "Over 20 years later, these injuries still bother me."

Panettiere said her opioid use subsequently increased when the old neck injury flared up.

She also described how her exposure to drugs had begun during her teenage years. At 16, Panettiere said somebody on her professional team offered her a "happy pill" before a red-carpet appearance.

Panettiere began requesting the pills regularly and later described them as a "gateway drug" to other substances.

Her addiction eventually included serious alcohol abuse. Panettiere wrote her drinking became so severe she developed jaundice and received a stark medical warning.

She wrote: "A doctor told me that if I didn't stop drinking, I'd be dead within five years."

Panettiere had also experienced significant emotional difficulties from childhood. She recalled being bullied at school before being homeschooled as her acting career accelerated.

Her memoir additionally contained allegations of inappropriate sexual behavior by unnamed Hollywood figures when she was 18 and 19.

Panettiere discussed addiction alongside motherhood, including her decision to transfer custody of her daughter Kaya, 11, to her former fiancé, Wladimir Klitschko, 50, after experiencing addiction and severe postpartum depression.

She wrote: "Kaya needed to feel at rest, not just physically, but mentally and emotionally."