Pallbearers carry the casket of actor Corey Haim from a memorial chapel in Toronto March 16, 2010. REUTERS/Mike Cassese

LOS ANGELES (Reuters) - Actor Corey Haim died of pneumonia and heart problems, and tests during an autopsy on his body found “no significant contributing factors” from drugs, the Los Angeles coroner’s office said on Tuesday.

Haim, a Canadian-born teen film star of the 1980s who had spoken openly about struggles with drug and alcohol addiction, collapsed at his Los Angeles apartment and died in a nearby hospital on March 10. He was 38.

Officials initially thought his death was due to a drug overdose. California law enforcement officials said he bought more than 550 doses of prescription painkillers and anti-anxiety drugs in the weeks before his death in what they linked to a big, illegal prescription drug ring.

But the coroner’s office said on Tuesday that Haim died of natural causes from a combination of pneumonia, respiratory and heart problems.

Ed Winter of the coroner’s office said that Haim’s mother found her son in distress in the middle of the night and he collapsed with flu-like symptoms. He was pronounced dead in the hospital less than an hour later.

Haim was best known for his work on the 1980s movies such as “Lucas” and “The Lost Boys”. He also worked with fellow teen star Corey Feldman on the U.S. television reality series “The Two Coreys” in 2007 and 2008.