She said: "I definitely went a bit bonkers in my early 20s, when I got famous quite quickly. Bonkers in a way where I didn't eat enough, I drank too much coffee, smoked too many cigarettes, cried a lot and was very emotional."
Minnie was pulled out of this difficult stage of her life by her sister, model-and-producer Kate, who told she was "acting like an idiot".
More celebrity gossip on IrishCentral
John Walker Lindh, the American Taliban, seeks Irish citizenship - POLL
Amy Adams to star in and produce movie of Steve Martin’s novel ‘Object of Beauty’
In an interview with Stylist magazine, the 'Hunky Dory' star revealed: "My sister showed up one day and said, 'I don't recognise you. You weigh seven stone and you're behaving like an idiot.' I came back to England and sorted myself out. Hollywood is portrayed in this super glamorous way, but when I see pictures of actresses going off the rails, it doesn't surprise me at all. You have to have solid family and friends."
Minnie - who has a three-year-old son, Henry - is now documenting her experiences in an autobiography.
She hopes the book will show people what it's really like to be an actress in Hollywood.
She said: "I'm working on a memoir about my childhood and getting famous, It's an interesting journey to tell if you haven't dissolved into drugs and alcohol. I want to tell it from the view of someone who was normal, but whose life became abnormal."