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.

RIP

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