Toxicology tests could take up to eight weeks.
Conaway died Friday morning at an Encino hospital after being in a coma for more than two weeks.
The actor had been battling pneumonia and sepsis, a type of bacterial blood poisoning. He was hospitalized May 11 when he was found unconscious from what his manager said was a drug overdose that may have involved pain pills.
Conaway had a long history of substance abuse. He was 60 years old.
Conaway appeared in the film "Grease" and the TV show "Taxi."
Funeral services for Conaway are pending.
City News Service contributed to this report.