“This was a group that was very, very tough,” Dr. Drew Pinsky recently told Entertainment Tonight, speaking about the newest season of his reality series Celebrity Rehab with Dr. Drew. He called the season “by far, the most difficult” he’s done to date.

Dennis Rodman, Mackenzie Phillips, Heidi Fleiss, Tom Sizemore, Mindy McCready, Lisa D’Amato, Mike Starr and Joey Kovar are part of the Rehab cast. The new season premieres January 7 on VH1.