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.
To help his recovery, Conaway was in a medically induced coma at the Encino Tarzana Medical Center, his manager Phil Brock said.
In 2008, the actor aired his battle with addiction on TV's "Celebrity Rehab." Conaway has struggled with back pain and repeated operations.
Dr. Drew Pinsky, who worked with Conaway on "Celebrity Rehab" released the following statement:
"There is no evidence showing Jeff died from an overdose. This was aspiration with overwhelming pneumonia and sepsis. Jeff is another example of a pharmaceutical death from the overutilization of prescription drugs. Please continue to pray for his friends and family. They appreciate your support."
John Travolta, who starred in "Grease" with Conaway, released a statement Friday: "Jeff Conaway was a wonderful and decent man and we will miss him. My heartfelt thoughts are with his family and loved ones at this very difficult time."
Funeral services for Conaway are pending.