The 38-year-old Lost Boys actor, who died on March 11 after collapsing in his LA apartment, was previously rumoured to have died from a drug overdose.
Us Magazine quotes the Los Angeles Department of Coroners' report as saying that drugs were "no significant contributing factors" in his death.
The coroner listed possible causes of death as pneumonia, damaged air sacs in the lungs and a build-up in blood vessels and the heart.
Haim's funeral took place in his hometown of Toronto on March 16.
