Reese Witherspoon has told Sky News her latest film is the hardest she has made so far in her career.
The actress has been tipped for an Oscar nomination for her portrayal of a woman who hiked the Pacific Crest Trail alone for three months to cope with the death of her mother, the breakdown of her marriage and her heroin addiction.
Wild sees Cheryl Strayed battle through desert heat, record snowstorms and driving rain while carrying a giant backpack.
Witherspoon, 38, was joined by Strayed, whose memoir the film is based on, for the film's outing as part of the BFI London Film Festival in Leicester Square.
Cheryl Strayed sold the rights to her book to Witherspoon
Witherspoon said: "It was more challenging in a way that I've never had before. It's definitely the hardest movie I've ever made, physically, emotionally, mentally, but when I got through it I was so happy."
The role involved going make-up free and she said: "The no make-up thing I didn't think about at all. They covered up all the mirrors in the make-up trailer so I didn't really know how I looked and it became sort of like a documentary. I wasn't the only person there filming, but I felt all alone."