Fitness Influencer Hayley McNeff’s Cause of Death Revealed After Dying at Age 37

Hayley McNeff’s cause of death has been revealed.

The fitness influencer died from “acute intoxication due to the combined effects of heroin, fentanyl, 4-ANPP, cocaine and norbuprenorphine,” Director of Communications for Massachusetts’s Executive Office of Public Safety and Security, Brenna Galvin, told People in a statement on Monday, November 10.

Galvin ruled McNeff’s death an accident, per the report.

Us Weekly has reached out for comment.

News broke in August that McNeff, a bodybuilder, died at the age of 37.

“Such a bright light has left this world too soon with the unexpected but peaceful passing of Hayley C. McNeff on August 8, 2025,” an obituary published by Boston.com read days later.

The obituary continued: “A lifelong athlete, she excelled as an accomplished equestrian, a talented board diver and skier as a youth and young adult. As an adult, she discovered a passion for bodybuilding and was the US Bodybuilding Champion during her career. She later pursued graduate studies in psychology, driven by a desire to better understand and help others.”

McNeff, who amassed more than 2,000 followers via Instagram for her fitness expertise, was praised for her “quick wit” and “sense of humor.”

“Her energy and determination was a constant in her life and she always accomplished what she set out to achieve,” the message read. “She treasured her friendships and nurtured strong, lasting relationships with those who knew her best. Hayley will be deeply missed by her parents, siblings, extended family, and friends.”

Hayley’s father, Dave McNeff, called his late daughter a “beam of light,” who had “boundless energy.”

“[She] was very determined to achieve whatever she set out to do,” he told People in a statement at the time. “She set her sights on bodybuilding and fitness and achieved the highest success that sector offered. She loved us and we love Hayley very much, we miss her madly.”

Fellow body builder Dave Palumbo also paid tribute to Hayley in August, remembering her for her part in 2916’s Raising the Bar documentary.

“I’m sad to hear of the passing of former woman bodybuilder @hayleysmash (HAYLEY MCNEFF) … she left us way too soon,” Palumbo, 57, wrote via Instagram. “She was a good soul, super intelligent and had tremendous potential as a bodybuilder. She appeared in @dave_pulcinella RAISING THE BAR videos back in the day and I was proud to be able to call her a friend. Prayers to her family and friends. R.I.P. @official_rxmuscle.”

Hayley’s friends and loved ones said their goodbyes to the late influencer on August 16, according to her obituary. A visitation was held in Wellesley, Massachusetts, followed by a funeral service.

In wake of her death, the obituary stated that donations could be made to National Alliance on Mental Illness Massachusetts in her honor.