Whitney Houston Cause of Death: Coroner -- Whitney Was Coked Up At Time of Death

An official for the L.A. County Coroner's Office just stated ... Whitney Houston used cocaine immediately prior to her death.

Coroner Chief Craig Harvey just held a news conference -- claiming the toxicology results suggested Whitney was a "chronic" cocaine user.

Harvey described the cocaine level in Whitney's system as "acute" -- indicating Whitney used the drug not long before she accidentally drowned in a bathtub at the Beverly Hilton hotel last month. "Accidental drowning" is listed as Whitney's official cause of death.

According to Harvey, the autopsy revealed a 60% narrowing of Whitney's arteries -- a direct result of the chronic cocaine use. Harvey claims the artery constriction led to a cardiac event before her death.

As for the other drugs in her system -- marijuana, Benadryl, Flexeril, and Xanax -- which Harvey claims were all at or below therapeutic levels ... and did not significantly contribute to her death.