A spokesman for the L.A. County Coroner's office says they are waiting for toxicology tests before determining the cause of death.
Haim had struggled with drug addiction for decades.
Haim died Wednesday in Burbank after collapsing at his mother's apartment in Universal City. According to the LAPD, Haim had been staying with his mother for about a year.
Friends and neighbors say that Haim shared acting advice with some of the young actors that lived in the apartment complex.
One neighbor said that Haim always looked young and healthy, but that he was under a lot of stress taking care of his mother who has been ill.
"First she had cancer which was hard on him," said Eric Jay. "He loved his mom and they were very close. They are in my prayers."
He earned fame for roles in the 1980s films "Lucas" and "The Lost Boys." He recently completed several film projects.