John Phillips poses for a photograph December 1, 1980 with his daughter MacKenzie while in drug rehab at Fair Oaks Hospital in Summit, New Jersey.
Mackenzie Phillips own family might be questioning the validity of her claims that her father, John Phillips, sexually abused her, but "Celebrity Rehab's" Dr. Drew Pinsky, who has treated Mackenzie, is firmly in her corner.
"I know Mackenzie to be practicing a rigorous program of honesty," Dr. Drew told Access Hollywood on Wednesday. "She would not be sober right now if she were not being completely honest all the time. She may have had distortions about that relationship but there is no doubt whatever happened severely traumatized her."
Dr. Drew explained that he's not surprised that some members of Mackenzie's family, stepmoms Genevieve Phillips and Michelle Phillips, have spoken out against her claims. (Half-sister Chynna Phillips has reportedly said she believes Mackenzie.)
"I'm sure the family [has] very conflicted feelings about this," he continued. "There may be aspects of this that are inaccurate but there is just no doubt in my mind that Mackenzie had severe trauma growing up and I didn't find any other sources of trauma than this in my work with her."
As for the timing of the shocking allegations she makes in her new book, "High On Arrival," Dr. Drew said it could be about settling the score with her late father.
"I get the feeling that she's needed to tell the story for some time. She talked a little bit about how conflicted she was about how people idealized her father and really shamed her for being an addict," he explained. "In a way, she may need to set the score right."
Dr. Drew, who treated Mackenzie during Season 3 of "Celebrity Rehab," said he is concerned for the future of Mackenzie's recovery, but said that is the case with anyone struggling with addiction.
"Right now my experience of her is that she is solid in recovery," he said. "If anything, we've seen recently how slippery and cunning an addiction is. DJ AM could not have been a more sober guy, he dies of addiction. So every day Mackenzie has to struggle with her disease."
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PLAY IT NOW: Dr. Drew: Mackenzie Phillips Is Practicing 'A Rigorous Program Of Honesty'
PLAY IT NOW: Mackenzie Phillips Reveals Incestuous Relationship With Her Father