Conaway in coma after apparent OD

Jeff Conaway, the actor who rose to fame in "Grease" and "Taxi" but has been known more recently for appearances on "Celebrity Rehab With Dr. Drew," was in a coma Thursday after an apparent drug overdose.

Conaway, 60, was unconscious and hospitalized with pneumonia at Encino Hospital Medical Center, family members told the Los Angeles Times.

"He turned his head two days ago, but nothing since," manager Phil Brock told E! News.

The actor -- who was Kenickie in the film version of "Grease" after playing Danny Zuko, the John Travolta character, on Broadway -- had struggled with substance abuse for decades, first seeking treatment in the late 1980s. His most recent high-profile acting work was in the late '90s on "Babylon 5."

Conaway was hospitalized for a broken hip in January 2010 after a fall at his home. "Jeff thinks these are his final days," then-girlfriend Vikki Lizzi told E! News at the time, while Brock said the hip surgery was the culmination of four months of health problems resulting from a previous fall.

Before that, Conaway appeared on "Celebrity Rehab," having developed an addiction to cocaine and pain pills after undergoing back surgery, he said. According to the Los Angeles Times' Amy Kaufman, as he attempted to quit those drugs on the program, he threw tantrums, shouted and blacked out -- but later said he'd ramped up his antics for the camera.

Mackenzie Phillips urged people via Twitter to "all say a prayer (or whatever works 4 you) for Jeff Conaway tonight." The "One Day at a Time" actress appeared on the third season of "Celebrity Rehab."