The King of Pop, who was allegedly being treated for insomnia, had lethal levels of the strong anaesthetic Propofol in his body when he died, according to court papers.
Details of the coroners' findings were revealed when a search warrant affidavit was made public in Texas, reports the Sun.
Investigators have quizzed the team of doctors who treated Jackson, including his personal physician Dr Conrad Murray [ Images ], who, though not named as a suspect, is at the centre of a manslaughter probe.
A search warrant affidavit for Murray in California read: 'The Los Angeles Chief Medical Examiner-Coroner, Dr Sathyavagiswaran, indicated that he had reviewed the preliminary toxicology results and his preliminary assessment of Jackson's cause of death was due to lethal levels of propofol (diprivan).'
The affidavit apparently revealed that Murray told LAPD detectives he had been giving the singer propofol as part of his treatment for insomnia, and feared the star was becoming addicted to the drug.
But Murray, who has denied any wrong doing, reportedly gave Jackson a lower dosage of propofol on the morning of his death after several other drugs failed to work.
Jackson died aged 50 from an apparent cardiac arrest at his rented LA mansion on June 25.
Image: Houston Police put out crime scene tape as Drug Enforcement Agents (DEA) and Los Angeles police detectives carry out a search warrant at the office of Conrad Murray, the doctor who was with the pop icon when he died, at Armstrong Medical Clinic in Houston.
Text: ANI | Photograph: Richard Carson/Reuters