Sept. 23, 2009 -- Former child-star Mackenzie Phillips, whose life has been marred by drug abuse and arrests, confessed today that she engaged in a 10-year consensual sexual relationship with her father, rock star John Phillips.

Phillips, 49, the former star of '70s-'80s sitcom "One Day at a Time," told Oprah Winfrey that she was first raped by her father in a hotel room when she was 18 while passed out after a drug binge but continued to use drugs and have consensual sex with him for years.

The relationship continued long after she married Jeff Sessler when she was 19, and ended only when she became pregnant and feared her father was the baby's father, Phillips said. John Phillips, she said, paid for an abortion.

Reading an excerpt from her new book, "High on Arrival," on Winfrey's show today, Phillips said of her first sexual experience with her father: "I woke up that night from a blackout to find myself having sex with my father. I don't know how it started."

She was raped by her father, lead singer of the Mamas and the Papas, in the hotel room in the late 1970s, Phillips said.

"For a moment, I was in my body for a horrible truth," she said of waking up and realizing she had had sex with her father.

"I boxed it away. I started very early on in my life compartmentalizing. ... This was the mother of all difficult experiences. ... I [have spent] the last 30 years trying not to look at it," she said.

Michelle Phillips, Mackenzie Phillips' stepmother and a member of the '60s group the Mamas and the Papas, told the Hollywood Reporter she believed the allegations were false.

Phillips said Mackenzie had "a lot of mental illness" and that "she's had a needle stuck up her arm for 35 years."

"Mackenzie is jealous of her siblings, who have accomplished a lot and did not become drug addicts," Michelle said.

Mackenzie Phillips told Winfrey she confronted her father about the rape, but he characterized their relationship as romantic, Mackenzie said.

"After the first experience, I went to my father and said we need to talk about how you raped me. My dad said: 'Raped you? Don't you mean made love?' In that moment, I thought I'm really on my own here."

In 1980, soon after she'd been fired from "One Day at a Time" because of her out-of-control drug use, Phillips began to travel with her father's new band, the New Mamas and the Papas. It was during that time, she said, that she began regularly doing drugs and having sex with her father.

"It didn't happen every day, it didn't happen every week, but it certainly happened and happened many times," she said.

Mackenzie Phillips Forgave Her Father

"It became a consensual relationship over time. I can't believe I'm the only one this happened to," she said.

"No matter what kind of incest, it is an abuse of power ... a betrayal of trust."

She forgave her father on his deathbed, but his death, in 2001, relaunched her abuse of drugs, Phillips said.

In excerpts from "High on Arrival" printed in People magazine, Phillips writes: "On the eve of my wedding, my father showed up, determined to stop it. I had tons of pills and dad had tons of everything too. Eventually I passed out on Dad's bed.

"I was a fragment of a person, and my secret isolated me," she writes, according to People. "One night Dad said, 'We could just run away to a country where no one would look down on us. There are countries where this is an accepted practice. Maybe Fiji.'"

Phillips was supposed to be reunited last year with her former television co-stars on the "Rachael Ray Show" but was arrested at Los Angeles International airport for possessing cocaine.

Former co-star Valerie Bertinelli learned of Phillip's incestuous relationship while backstage during the taping of the Winfrey show.

"You're only as sick as your secrets," Bertinelli told her old friend and said she regretted not being there to help Phillips earlier.

Phillips hails from a famous Hollywood family. Her sisters are singer-actress Bijou Phillips and Chynna Phillips. She has been married three times and has one son, born in 1997.