Champion Bodybuilder Hayley McNeff Cause of Death Released

Hayley McNeff’s death rocked the bodybuilding community over the summer -- and TMZ’s learned her cause of death was a drug overdose.

The Massachusetts Executive Office of Public Safety and Security has revealed Hayley’s death was caused by acute intoxication from a deadly mix of heroin, fentanyl, 4-ANPP, cocaine, and norbuprenorphine.

The manner of her death, which occurred back in August, was officially listed as accidental.

The fitness influencer made her mark on the bodybuilding scene in the 2000s -- racking up titles, including a big win at the 2009 East Coast Classic -- and later appeared in the 2016 documentary "Raising The Bar."

She was just 37 years old at the time of her death.