Blake Garrett, Child Actor in 'How to Eat Fried Worms,' Cause of Death Revealed

Blake Garrett -- best known for his role in "How to Eat Fried Worms" -- died from a fentanyl overdose ... TMZ has learned.

According to the Oklahoma Office of the Chief Medical Examiner's summary report, obtained by TMZ, the former child actor died from acute fentanyl toxicity ... with the manner of death ruled an accident. The report also notes Garrett died at a sober living house in Tulsa.

As TMZ first reported, Blake died back in February at just 33 years old. Blake's mom, Carol Garrett, told us at the time he'd recently been diagnosed with shingles ... and she believed he may have accidentally overdosed while trying to manage the pain after three years of sobriety.

Blake -- who was born in Austin, Texas -- built an impressive acting résumé before most kids finished elementary school. He landed early lead roles in local productions, including "Aladdin and His Magical Lamp" and "Peanuts: A Charlie Brown Tribute," before joining "Barney's Colorful World International Tour" at just 10 years old.

His biggest break came in 2006, when he played Plug in "How to Eat Fried Worms" -- a performance that earned him a Young Artist Award for Best Young Ensemble Cast.