In Melissa Explains it All, which hits bookshelves at the end of next month (Oct13), Hart opens up about her secret drug abuse hell and claims Hilton once offered her cocaine at a party - something the socialite's publicist insists the actress has misremembered.
Talking about the dark moments in the book, the Tv star tells Life & Style magazine, "I experimented with weed, Ecstasy, mushrooms and mescaline for about a year and a half. I was kind of running with a bad crowd. I just didn't enjoy taking drugs. I don't like the loss of control."
She reveals she once took Ecstasy at the Playboy Mansion in 1999 and made out with an unnamed woman in the limo ride home.
But it's her revelations about a party at Hilton's home, where the socialite allegedly offered her cocaine, that is set to really shock readers.
A rep for Paris has denied the claim.
And she's not the only celebrity who will be upset with Hart over her revelations - she also opens up about past flings with Jerry O'Connell and Backstreet Boys star Nick Carter, and she rips Ashton Kutcher for being a "smart a**", explaining she twice tried to kick him out of her parties for being a wiseguy.
She says, "Ashton and I just didn't get along."