Mackenzie Phillips believes she had `` genetic predisposition '' to substance abuse . Dad showed her how to roll joint when she was 10 , she tells Watch Mackenzie Phillips . Drug abuse forced her out of role on successful CBS sitcom ` Then , on Wednesday , the 49-year-old actress revealed on `` The Oprah Winfrey Show '' that she engaged in an incestuous relationship with her father , legendary musician John Phillips , for nearly 10 years . ` One Day at a Time '' `` Today '' show on Mackenzie Phillips , 10 Switzerland ET .
Mackenzie Phillips believes she had `` genetic predisposition '' to substance abuse . Dad showed her how to roll joint when she was 10 , she tells Watch Mackenzie Phillips . Drug abuse forced her out of role on successful CBS sitcom `` One Day at a Time '' `` Today '' show on Mackenzie Phillips , 10 Switzerland ET .