Assistant chief coroner Ed Winter said the request is made in virtually all death investigations because it can shed additional light on how people died and whether they had any serious medical conditions.
"We've already contacted a number of doctors with requests for records," he said.
Winter said that at this point, there is nothing unusual about how his office is proceeding with the Houston death investigation.
Investigators found several bottles of prescription medication in the Beverly Hills, California, hotel room where Houston died Saturday.
Winter has said they weren't an unusually large number. Detectives have declined to disclose which medications were found.
Authorities said an autopsy found no indications of foul play or obvious signs of trauma. Houston was underwater and apparently unconscious when she was pulled from a bathtub, officials said.
It could be weeks before the coroner's office completes toxicology tests to establish the cause of death.
Houston died just hours before she was scheduled to perform at producer Clive Davis' pre-Grammy Awards party. Her family plans a private church service Saturday in her hometown of Newark, New Jersey.
Houston, a sensation from her first album in 1985, was one of the world's best-selling artists from the mid-1980s to the late 1990s, turning out such hits as I Wanna Dance With Somebody, How Will I Know, The Greatest Love of All and I Will Always Love You.
But as she struggled with drugs, her majestic voice became raspy, and she couldn't hit the high notes.
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