His roommate found the 50-year-old dead in his Richmond home in March.
The Virginia State Medical Examiner's Office said on Tuesday that Brockie died from "acute heroin toxicity and the manner of death is accident.”
Remembered: Stars We've Lost
Brockie -- who went by the stage name “Oderus Urungus,” a 43-billion-year-old alien -- formed the “satirical thrash metal band” GWAR in Richmond in 1984. The group hit it big in the '90s and was known for their science fiction and horror-inspired costumes and shows.