Actress Reese Witherspoon. Photo / Getty Images

Reese Witherspoon has revealed she hired a hypnotist to help soothe her nerves before filming racy sex scenes in her new film Wild.

In a cover interview for Vogue, Witherspoon said that even the drug scenes in the big-screen adaptation of Cheryl Strayed's memoir were not as tough to shoot as the ones involving lovemaking.

And according to the article, the 38-year-old actress "employed a hypnotist to help quell her nerves" before doing the deed on screen.

Witherspoon hasn't done a nude scene since her role in 1998's Twilight, starring Gene Hackman, Susan Sarandon and Paul Newman.

But even though it's been a long time between drinks, the Legally Blonde star said she wanted to step out of her comfort zone for the role.

"I just didn't want to hear, 'Oh, we don't want to see Reese have sex ... Oh, can we not have any profanity?'," she told the magazine's October issue.

"I wanted it to be truthful. I wanted it to be raw, I wanted it to be real."

Oscar buzz has been surrounding Witherspoon since Wild, directed by Jean-Marc Vallee, screened at the Toronto Film Festival earlier this month.

In the movie, Strayed self-destructs after the death of her mother - destroying her marriage, getting hooked on heroin and even falling pregnant to a stranger.

Reese Witherspoon in Wild. Photo / AP

Strayed herself showed Witherspoon on set how to shoot up heroin for the grittier scenes, while Vallee said the actress' attitude to on-screen sex was refreshing.

"She'd never done a scene like this before," said Vallee, who added that he remembered her wondering, "Am I doing the right thing?" right up until he called action."It's not about her showing off and trying to do the ultimate performance. It's just her: 'I'm almost naked here, and I'm a 37-year-old, and I'm not perfect but it's all right. All right, let's do it.

"Witherspoon has one Oscar to her name, having won the best actress gong in 2006 for her role as Johnny Cash's wife June Carter Cash.

- AAP