The powerful sedative Diprivan was found in Michael Jackson's home, a law enforcement official said Friday.
Diprivan is an anesthetic widely used in operating rooms to induce unconsciousness.
Also known as Propofol, it's administered intravenously and is very unusual to have in a private home.
The law enforcement official spoke on condition of anonymity because the person was not authorized to speak about the matter.
Authorities are investigating allegations that the 50-year-old Jackson had been consuming painkillers, sedatives and antidepressants. Any criminal charges would depend on whether Jackson had been overly prescribed medications, given drugs inappropriate for his needs, or if doctors knowingly prescribed Jackson medications under an assumed name.
As Jackson prepared for a massive series of comeback concerts, he was so distraught over persistent insomnia that he for Diprivan, according Cherilyn Lee, a registered nurse who was working with the singer.
Lee said she repeatedly rejected his demands because the drug was unsafe.
It's still not known what caused Jackson's death on June 25. The pop star went into cardiac arrest in his bedroom and his personal physician, Dr. Conrad Murray, performed CPR while an ambulance was called, according to Murray's lawyers.
Murray has spoken to police and authorities say he is not a suspect.
An autopsy was conducted but results are not expected for several weeks. The Jackson family had a second autopsy performed and those results also are pending.