The Clueless star, 32, was found unresponsive in her Hollywood Hills home on Dec. 20, despite frantic attempts by her husband, Simon Monjack, and her mother, Sharon, to revive her.
Chief Coroner Investigator Craig Harvey specified that pneumonia was the primary cause of death, with drugs and anemia as contributing factors.
Simon and Sharon said they believed Brittany's death was due to a congenital heart murmur and denied rumors that the actress used illegal drugs or suffered from an eating disorder. They added that Murphy's heart condition was diagnosed in her teens, but said she had received proper treatment for it. They also said that she'd been suffering from laryngitis and flu-like symptoms in the days before her death.
A number of prescription meds were reportedly found by investigators on her nightstand. Simon says his wife was taking the painkiller Vicoprofen and the antidepressant Fluoxetine (also known as Sarafem) to deal with severe menstrual cramps, and that many of the other meds found were for his own use due to a seizure he recently suffered.
The actress was laid to rest in a twilight ceremony in Los Angeles on Christmas Eve.
A full autopsy report is expected within two weeks.