Media reports about possible drug use by US pop star Michael Jackson the day he died prompted a warning from anaesthesiologists today, as lawyers prepared to square-off in a courtroom battle over his estate.

Reports of prescription drug use have increasingly surfaced since the Thriller singer's sudden cardiac arrest more than one week ago, and a police probe is said to be focusing on the role doctors may have played in providing Jackson with at least one powerful medication, anaesthetic Diprivan, according to the Los Angeles Times.

Investigators are trying to determine if the drugs, which were found in searches of Jackson's rented Los Angeles mansion, were improperly prescribed and if they had a role in the June 25 death of the King of Pop at age 50.

Numerous bottles, of Diprivan without labels were found at the mansion, according to the Los Angeles Times. Diprivan, the brand name of propofol, is an anaesthetic that "should never be used outside of a controlled and monitored medical setting," the American Society of Anaesthesiologists (ASA) said in a statement, noting that its members have not studied the particulars of Jackson's death.

Patients can have extremely variable responses to the drug and some patients can become completely anaesthetised, including losing the ability to breathe, the group said. Two autopsies were performed on Jackson after his death but toxicology results are not expected for weeks. - Reuters