Jeff Conaway is in critical condition following an apparent overdose. The actor who rose to fame thanks to his roles in Grease and the TV series Taxi is currently unconscious and being treated at Encino Hospital Medical Center for pneumonia. Conaway is no stranger to substance abuse problems having began using drugs in the mid-1980s. He appeared on Celebrity Rehab with Dr. Drew where he sought treatment for addictions to cocaine, painkillers and alcohol. On the show he frequently threatened to quit and refused to end his relationship with his co-dependent girlfriend who also used prescription opiates.