At the autopsy , eight milligram percent of Chloral Hydrate and 4.5 milligram percent of Nembutal were found in her system . Dr. Thomas Noguchi of the Los Angeles County Coroners office stated the cause of death as `` acute barbiturate poisoning , '' resulting from a `` probable suicide '' . At the subsequent autopsy , eight milligram percent of Chloral hydrate and 4.5 milligram percent of Nembutal were found in her system , and Dr. Thomas Noguchi of the Los Angeles County Coroners office recorded cause of death as `` acute barbiturate poisoning '' , resulting from a `` probable suicide '' .