The British screenwriter, 40, was found dead May 23 at the couple's Hollywood home, five months after Murphy, 32, died.
The coroner's office said pneumonia was the primary cause of Murphy's death but anemia and multiple drug intoxication were contributing factors.
Asked for the cause of death for Monjack, Coroner Assistant Chief Ed Winter told CNN, "Just like Brittany." Winter added that some prescription drugs were found in his system but not in lethal levels.
At Monjack's family's request, another test will be conducted before the full autopsy report will be released, says Winter.