Lieut. Fred Corral, of the L.A. County Coroner's Office, says Elisa Lam's death was in part due to her bipolar disorder.
"Cause of death is listed as an accidental death due to drowning and other significant conditions: bipolar disorder."
Corral said in an interview Thursday that the woman's family has been alerted and the case has been closed.
When the 21-year-old student's body was found last February in a water cistern on top of the 600-room hotel near Skid Row, police called her death suspicious.
Before she died, hotel surveillance footage showed her inside an elevator pushing buttons and sticking her head out the doors as if she were looking for someone.
He body was discovered by a maintenance worker after guests complained about low water pressure, though later testing of the water found no contamination.
An autopsy after Lam's death was inconclusive, so officials said they would have to wait for toxicological tests.
Lam travelled alone to Los Angeles on Jan. 26 and was last seen five days later by hotel workers.