The Dec. 20 death of the actress was accidental and likely could have been prevented if Murphy had seen a doctor sooner, Assistant Chief Coroner Ed Winter said.
Winter declined to specify what types of drugs were involved in her death and said further details would be released in several weeks when the report was completed.
He also said there was no evidence of wrongdoing.
Winter said Murphy’s community-acquired pneumonia was serious and proved lethal when combined with the medications and iron deficiency anemia.
Murphy died at age 32 after collapsing in her Hollywood Hills home. Her mother and husband have said the actress didn’t abuse prescription medications or have an eating disorder.
Attempts to reach them for further comment were not immediately successful.
Murphy’s husband, Simon Monjack, and her mother, Sharon Murphy, told investigators the actress had been experiencing flu-like symptoms in the days before she died.
Monjack told The Associated Press last month that his wife did take several prescriptions, including an anti-seizure drug, but did not abuse the medications.
He said she had been taking over-the-counter Robitussin for her recent sickness.
Dr. Michael Baden, a former chief medical examiner in New York City, said the quantities and type of drugs Murphy was taking were key to understanding how she died.
“One doesn’t die of pneumonia, usually, that quickly,” Baden said.
He said the use of some prescription medications can lead to pneumonia.
“It sounds more like it’s a drug-related than a natural pulmonary pneumonia,” said Baden, who did not work on the Murphy case but has served as an expert witness in numerous high-profile deaths.