Reese Witherspoon says leaving an abusive relationship changed who she was on a "cellular level."

The 41-year-old has admitted that leaving the past relationship, in which she was allegedly ''psychologically and verbally'' abused, had a ''profound'' affect on her.

In a candid interview with Oprah's O Magazine, the actress, who is now married to Jim Toth, with whom she has five-year-old son Tennessee,  was asked what the most difficult task in her life has been.

"For me, probably leaving an abusive relationship," she said. "A line got drawn in the sand and it got crossed, and my brain just switched and I knew it was going to be very difficult but I just couldn't go any further. But it was profound and I was young.''

Witherspoon, who also has two children with her ex-husband Ryan Phillippe, admitted the experience completely changed her as a person.

''I could never be the person I am today. It changed who I was on a cellular level, the fact that I stood up for myself.

"None of those leaving those situations ... it's wrought with self-doubt, particularly if someone damages your self-esteem."

"People say to me that knew me then, 'You're a completely different person.' I didn't have self-esteem. I'm a different person now and it's part of why I can stand up and say, 'yes, I'm ambitious' - because someone tried to take that from me before.''

Last year, after the Harvey Weinstein scandal broke, Witherspoon came forward with her own story of being sexually assaulted by a director when she was 16 years old.